diff --git a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ActiveNodeGateEndpointFilter.cs b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ActiveNodeGateEndpointFilter.cs
index 0590798..770bdd3 100644
--- a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ActiveNodeGateEndpointFilter.cs
+++ b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ActiveNodeGateEndpointFilter.cs
@@ -14,7 +14,19 @@ namespace ZB.MOM.WW.Health;
 public sealed class ActiveNodeGateEndpointFilter : IEndpointFilter
 {
     /// <summary>Default <c>Retry-After</c> value (seconds) advertised on a standby 503 response.</summary>
-    private const int RetryAfterSeconds = 5;
+    private const int DefaultRetryAfterSeconds = 5;
+
+    private readonly int _retryAfterSeconds;
+
+    /// <summary>Initializes a new <see cref="ActiveNodeGateEndpointFilter"/> using the default 5 s retry-after.</summary>
+    public ActiveNodeGateEndpointFilter()
+        : this(DefaultRetryAfterSeconds)
+    {
+    }
+
+    /// <summary>Initializes a new <see cref="ActiveNodeGateEndpointFilter"/>.</summary>
+    /// <param name="retryAfterSeconds">The <c>Retry-After</c> value (seconds) advertised on a standby 503 response.</param>
+    public ActiveNodeGateEndpointFilter(int retryAfterSeconds) => _retryAfterSeconds = retryAfterSeconds;
 
     /// <summary>
     /// Returns 503 (with <c>Retry-After</c>) when the resolved <see cref="IActiveNodeGate"/> reports
@@ -34,7 +46,8 @@ public sealed class ActiveNodeGateEndpointFilter : IEndpointFilter
 
         if (gate is { IsActiveNode: false })
         {
-            httpContext.Response.Headers.RetryAfter = RetryAfterSeconds.ToString();
+            httpContext.Response.Headers.RetryAfter =
+                _retryAfterSeconds.ToString(System.Globalization.CultureInfo.InvariantCulture);
             return Results.StatusCode(StatusCodes.Status503ServiceUnavailable);
         }
 
@@ -53,10 +66,15 @@ public static class ActiveNodeGateExtensions
     /// returns 503 with a <c>Retry-After</c> header when the node is a standby.
     /// </summary>
     /// <param name="builder">The endpoint convention builder to decorate.</param>
+    /// <param name="retryAfterSeconds">
+    /// The <c>Retry-After</c> value (seconds) advertised on a standby 503 response. Defaults to 5.
+    /// </param>
     /// <returns>The same <paramref name="builder"/> for chaining.</returns>
-    public static IEndpointConventionBuilder RequireActiveNode(this IEndpointConventionBuilder builder)
+    public static IEndpointConventionBuilder RequireActiveNode(
+        this IEndpointConventionBuilder builder,
+        int retryAfterSeconds = 5)
     {
         ArgumentNullException.ThrowIfNull(builder);
-        return builder.AddEndpointFilter(new ActiveNodeGateEndpointFilter());
+        return builder.AddEndpointFilter(new ActiveNodeGateEndpointFilter(retryAfterSeconds));
     }
 }
diff --git a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyHealthCheck.cs b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyHealthCheck.cs
index 0c577d8..e1aa4c2 100644
--- a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyHealthCheck.cs
+++ b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyHealthCheck.cs
@@ -58,11 +58,19 @@ public sealed class GrpcDependencyHealthCheck : IHealthCheck
                 ? HealthCheckResult.Healthy($"{name} is reachable.")
                 : HealthCheckResult.Unhealthy($"{name} is unreachable.");
         }
+        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+        {
+            throw;
+        }
+        catch (RpcException ex) when (ex.StatusCode == StatusCode.Cancelled && cancellationToken.IsCancellationRequested)
+        {
+            throw new OperationCanceledException(cancellationToken);
+        }
         catch (RpcException ex)
         {
             return HealthCheckResult.Unhealthy($"{name} probe failed: {ex.Status.StatusCode}.", ex);
         }
-        catch (OperationCanceledException ex) when (timeoutCts.IsCancellationRequested && !cancellationToken.IsCancellationRequested)
+        catch (OperationCanceledException ex) when (timeoutCts.IsCancellationRequested)
         {
             return HealthCheckResult.Unhealthy($"{name} probe timed out after {_options.Timeout}.", ex);
         }
diff --git a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyOptions.cs b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyOptions.cs
index bd42812..6bd0a0e 100644
--- a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyOptions.cs
+++ b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyOptions.cs
@@ -21,6 +21,21 @@ public sealed class GrpcDependencyOptions
     /// </summary>
     public string? DependencyName { get; set; }
 
+    private TimeSpan _timeout = TimeSpan.FromSeconds(5);
+
     /// <summary>Maximum time the probe may take before it is treated as unreachable. Default 5 s.</summary>
-    public TimeSpan Timeout { get; set; } = TimeSpan.FromSeconds(5);
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when set to a value &lt;= <see cref="TimeSpan.Zero"/>.</exception>
+    public TimeSpan Timeout
+    {
+        get => _timeout;
+        set
+        {
+            if (value <= TimeSpan.Zero)
+            {
+                throw new ArgumentOutOfRangeException(nameof(value), value, "Timeout must be greater than zero.");
+            }
+
+            _timeout = value;
+        }
+    }
 }
diff --git a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthResponseWriter.cs b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthWriter.cs
similarity index 88%
rename from ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthResponseWriter.cs
rename to ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthWriter.cs
index 8cbfe26..401626c 100644
--- a/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthResponseWriter.cs
+++ b/ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthWriter.cs
@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Diagnostics.HealthChecks;
 
@@ -28,6 +29,7 @@ public static class ZbHealthWriter
     private static readonly JsonSerializerOptions SerializerOptions = new()
     {
         PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
     };
 
     /// <summary>
@@ -35,7 +37,7 @@ public static class ZbHealthWriter
     /// </summary>
     /// <param name="context">The current HTTP context. Its <see cref="HttpResponse"/> is written to.</param>
     /// <param name="report">The aggregated health report for the tier that ran.</param>
-    public static Task WriteJsonAsync(HttpContext context, HealthReport report)
+    public static async Task WriteJsonAsync(HttpContext context, HealthReport report)
     {
         ArgumentNullException.ThrowIfNull(context);
         ArgumentNullException.ThrowIfNull(report);
@@ -56,7 +58,7 @@ public static class ZbHealthWriter
                 }),
         };
 
-        return context.Response.WriteAsync(JsonSerializer.Serialize(payload, SerializerOptions));
+        await JsonSerializer.SerializeAsync(context.Response.Body, payload, SerializerOptions, context.RequestAborted).ConfigureAwait(false);
     }
 
     private sealed class HealthReportDto
diff --git a/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Tests/GrpcDependencyHealthCheckTests.cs b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Tests/GrpcDependencyHealthCheckTests.cs
index d1dd117..33769e4 100644
--- a/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Tests/GrpcDependencyHealthCheckTests.cs
+++ b/ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Tests/GrpcDependencyHealthCheckTests.cs
@@ -14,14 +14,15 @@ public sealed class GrpcDependencyHealthCheckTests
 {
     private static readonly GrpcChannel Channel = GrpcChannel.ForAddress("http://localhost");
 
-    private static async Task<HealthCheckResult> RunAsync(GrpcDependencyOptions options)
+    private static async Task<HealthCheckResult> RunAsync(
+        GrpcDependencyOptions options, CancellationToken cancellationToken = default)
     {
         var check = new GrpcDependencyHealthCheck(Channel, options);
         var context = new HealthCheckContext
         {
             Registration = new HealthCheckRegistration("grpc-dep", check, HealthStatus.Unhealthy, tags: null),
         };
-        return await check.CheckHealthAsync(context, CancellationToken.None);
+        return await check.CheckHealthAsync(context, cancellationToken);
     }
 
     [Fact]
@@ -69,4 +70,38 @@ public sealed class GrpcDependencyHealthCheckTests
         Assert.Equal(HealthStatus.Unhealthy, result.Status);
         Assert.Contains("mxaccessgw worker", result.Description);
     }
+
+    [Fact]
+    public async Task ProbeExceedsTimeout_Unhealthy()
+    {
+        var result = await RunAsync(new GrpcDependencyOptions
+        {
+            Timeout = TimeSpan.FromMilliseconds(50),
+            Probe = static async (_, ct) =>
+            {
+                await Task.Delay(Timeout.Infinite, ct);
+                return true;
+            },
+        });
+
+        Assert.Equal(HealthStatus.Unhealthy, result.Status);
+    }
+
+    [Fact]
+    public async Task ExternalCancellation_Throws()
+    {
+        using var cts = new CancellationTokenSource();
+        await cts.CancelAsync();
+
+        await Assert.ThrowsAnyAsync<OperationCanceledException>(() => RunAsync(
+            new GrpcDependencyOptions
+            {
+                Probe = static async (_, ct) =>
+                {
+                    await Task.Delay(Timeout.Infinite, ct);
+                    return true;
+                },
+            },
+            cts.Token));
+    }
 }
diff --git a/components/health/shared-contract/ZB.MOM.WW.Health.md b/components/health/shared-contract/ZB.MOM.WW.Health.md
index 0f81a35..e786e78 100644
--- a/components/health/shared-contract/ZB.MOM.WW.Health.md
+++ b/components/health/shared-contract/ZB.MOM.WW.Health.md
@@ -73,7 +73,7 @@ public static class ZbHealthEndpointExtensions
         Action<ZbHealthEndpointOptions> configure);
 }
 
-/// Canonical JSON response writer. Shape: { status, totalDurationMs, entries: { name: { status, description, duration } } }.
+/// Canonical JSON response writer. Shape: { status, totalDurationMs, entries: { name: { status, description, durationMs } } }.
 public static class ZbHealthWriter
 {
     public static Task WriteJsonAsync(HttpContext context, HealthReport report);
diff --git a/components/health/spec/SPEC.md b/components/health/spec/SPEC.md
index 93224e0..b956c04 100644
--- a/components/health/spec/SPEC.md
+++ b/components/health/spec/SPEC.md
@@ -121,12 +121,12 @@ All health endpoints share one canonical JSON serializer. The shape is lifted fr
     "database": {
       "status": "Healthy",
       "description": "SQL Server reachable",
-      "duration": "00:00:00.0120000"
+      "durationMs": 12
     },
     "akka-cluster": {
       "status": "Healthy",
       "description": "Member status: Up",
-      "duration": "00:00:00.0001000"
+      "durationMs": 0.1
     }
   }
 }
@@ -141,7 +141,7 @@ All health endpoints share one canonical JSON serializer. The shape is lifted fr
 | `entries` | object | Keyed by check registration name |
 | `entries.<name>.status` | string | Per-check status |
 | `entries.<name>.description` | string? | Human-readable detail (may be null) |
-| `entries.<name>.duration` | string | TimeSpan `ToString()` — per-check elapsed time |
+| `entries.<name>.durationMs` | number | Per-check elapsed time, milliseconds |
 
 The writer is exposed as a static `Task WriteJsonAsync(HttpContext, HealthReport)` so consumers can
 plug it into `MapHealthChecks` options and also call it from custom endpoints.