diff --git a/docs/requirements/Component-ExternalSystemGateway.md b/docs/requirements/Component-ExternalSystemGateway.md
index dd3c4dd6..1540528a 100644
--- a/docs/requirements/Component-ExternalSystemGateway.md
+++ b/docs/requirements/Component-ExternalSystemGateway.md
@@ -35,7 +35,7 @@ Each external system definition includes:
 - **Authentication**: One of:
   - **API Key**: Header name (e.g., `X-API-Key`) and key value.
   - **Basic Auth**: Username and password.
-- **Timeout**: Per-system timeout for all method calls (e.g., 30 seconds). Applies to the HTTP request round-trip.
+- **Timeout**: Per-system timeout for all method calls (e.g., 30 seconds). Applies to the HTTP request round-trip. `0` (the default) means "unset" — the gateway's configured `DefaultHttpTimeout` applies instead. Set via the Central UI External System form's "Timeout (seconds)" field; ships to sites in the deployment artifact like the other definition fields.
 - **Retry Settings**: Max retry count, fixed time between retries (used by Store-and-Forward Engine for transient failures only).
 - **Method Definitions**: List of available API methods, each with:
   - Method name.
@@ -98,7 +98,7 @@ Scripts choose between two call modes per invocation, mirroring the dual-mode da
 
 ## Call Timeout & Error Handling
 
-- Each external system definition specifies a **timeout** that applies to all method calls on that system.
+- Each external system definition specifies a **timeout** (`TimeoutSeconds`) that applies to all method calls on that system. `0` means unset — the gateway's configured `DefaultHttpTimeout` applies instead. Editable via the Central UI External System form ("Timeout (seconds)", helper text "0 = use gateway default") and deployed to sites in the artifact alongside the rest of the definition.
 - Error classification by HTTP response:
   - **Transient failures** (connection refused, timeout, HTTP 408, 429, 5xx): Behavior depends on call mode — `CachedCall` buffers for retry; `Call` returns error to script.
   - **Permanent failures** (HTTP 4xx except 408/429): Always returned to the calling script regardless of call mode. Logged to Site Event Logging. For `CachedCall`, the failure is additionally recorded as a terminal `Failed` tracking record — so even a never-buffered cached call has an authoritative status record.
diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Design/ExternalSystemForm.razor b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Design/ExternalSystemForm.razor
index 35acb1f5..5834a568 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Design/ExternalSystemForm.razor
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Design/ExternalSystemForm.razor
@@ -62,6 +62,11 @@
                     <label class="form-label">Retry Delay (seconds)</label>
                     <input type="number" class="form-control" @bind="_retryDelaySeconds" min="0" />
                 </div>
+                <div class="mb-3">
+                    <label class="form-label">Timeout (seconds)</label>
+                    <input type="number" class="form-control" @bind="_timeoutSeconds" min="0" />
+                    <div class="form-text">0 = use gateway default</div>
+                </div>
 
                 @if (_formError != null)
                 {
@@ -85,6 +90,7 @@
     private string? _authConfig;
     private int _maxRetries = 3;
     private int _retryDelaySeconds = 5;
+    private int _timeoutSeconds;
     private string? _formError;
 
     private ExternalSystemDefinition? _existing;
@@ -112,6 +118,7 @@
                     _authConfig = _existing.AuthConfiguration;
                     _maxRetries = _existing.MaxRetries;
                     _retryDelaySeconds = (int)_existing.RetryDelay.TotalSeconds;
+                    _timeoutSeconds = _existing.TimeoutSeconds;
                 }
             }
             catch (Exception ex) { _formError = ex.Message; }
@@ -138,6 +145,7 @@
                 _existing.AuthConfiguration = _authConfig?.Trim();
                 _existing.MaxRetries = _maxRetries;
                 _existing.RetryDelay = TimeSpan.FromSeconds(_retryDelaySeconds);
+                _existing.TimeoutSeconds = _timeoutSeconds;
                 await ExternalSystemRepository.UpdateExternalSystemAsync(_existing);
             }
             else
@@ -146,7 +154,8 @@
                 {
                     AuthConfiguration = _authConfig?.Trim(),
                     MaxRetries = _maxRetries,
-                    RetryDelay = TimeSpan.FromSeconds(_retryDelaySeconds)
+                    RetryDelay = TimeSpan.FromSeconds(_retryDelaySeconds),
+                    TimeoutSeconds = _timeoutSeconds
                 };
                 await ExternalSystemRepository.AddExternalSystemAsync(es);
             }
diff --git a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Design/ExternalSystemFormAuditDrillinTests.cs b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Design/ExternalSystemFormAuditDrillinTests.cs
index b2e78746..3070dce0 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Design/ExternalSystemFormAuditDrillinTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Design/ExternalSystemFormAuditDrillinTests.cs
@@ -1,3 +1,4 @@
+using System.Linq;
 using System.Security.Claims;
 using Bunit;
 using Microsoft.AspNetCore.Components;
@@ -67,4 +68,65 @@ public class ExternalSystemFormAuditDrillinTests : BunitContext
             Assert.Empty(cut.FindAll("a[data-test=\"audit-link\"]"));
         });
     }
+
+    [Fact]
+    public void Form_RendersTimeoutSecondsInput_WithGatewayDefaultHelperText()
+    {
+        // PLAN-06 Task 12: the per-system TimeoutSeconds column (Task 8) needs a
+        // Central UI form field so Design users can actually set it.
+        var cut = Render<ExternalSystemForm>();
+
+        cut.WaitForAssertion(() =>
+        {
+            Assert.Contains("Timeout (seconds)", cut.Markup);
+            Assert.Contains("0 = use gateway default", cut.Markup);
+        });
+    }
+
+    [Fact]
+    public void SavingNewSystem_WithTimeoutSeconds_PassesTimeoutSecondsToRepository()
+    {
+        var cut = Render<ExternalSystemForm>();
+
+        // Re-query between each Change(): two-way binding re-renders the form and
+        // invalidates previously found element references.
+        cut.FindAll("input[type=text]")[0].Change("ERP-Beta");                          // Name
+        cut.FindAll("input[type=text]")[1].Change("https://erp-beta.example.test");     // Endpoint URL
+        cut.FindAll("input[type=number]")[2].Change("20");                              // Timeout (seconds)
+
+        cut.FindAll("button").First(b => b.TextContent.Contains("Save")).Click();
+
+        cut.WaitForAssertion(() =>
+        {
+            _repo.Received().AddExternalSystemAsync(
+                Arg.Is<ExternalSystemDefinition>(e => e.TimeoutSeconds == 20));
+            _repo.Received().SaveChangesAsync();
+        });
+    }
+
+    [Fact]
+    public void SavingEditedSystem_UpdatesTimeoutSecondsOnExisting()
+    {
+        var existing = new ExternalSystemDefinition("ERP-Delta", "https://erp-delta.example.test", "ApiKey")
+        {
+            Id = 11,
+            TimeoutSeconds = 10,
+        };
+        _repo.GetExternalSystemByIdAsync(11, Arg.Any<CancellationToken>()).Returns(existing);
+
+        var cut = Render<ExternalSystemForm>(p => p.Add(c => c.Id, 11));
+        cut.WaitForState(() => cut.FindAll("input[type=number]").Count >= 3);
+
+        // The Timeout field must be pre-filled from the existing entity on load.
+        Assert.Contains(cut.FindAll("input[type=number]"), i => i.GetAttribute("value") == "10");
+
+        cut.FindAll("input[type=number]")[2].Change("60"); // Timeout (seconds)
+        cut.FindAll("button").First(b => b.TextContent.Contains("Save")).Click();
+
+        cut.WaitForAssertion(() =>
+        {
+            Assert.Equal(60, existing.TimeoutSeconds);
+            _repo.Received().UpdateExternalSystemAsync(existing);
+        });
+    }
 }