diff --git a/Source/Testably.Abstractions.Migration.Analyzers/Patterns.cs b/Source/Testably.Abstractions.Migration.Analyzers/Patterns.cs
index 1db5a3e..49d16c8 100644
--- a/Source/Testably.Abstractions.Migration.Analyzers/Patterns.cs
+++ b/Source/Testably.Abstractions.Migration.Analyzers/Patterns.cs
@@ -57,6 +57,19 @@ public static class Patterns
 	/// </summary>
 	public const string MockFileSystemAddDrive = "MockFileSystem.AddDrive";
 
+	/// <summary>
+	///     <c>fs.MockTime(Func&lt;DateTime&gt;)</c>. Manual review (Phase 5.3): TestableIO
+	///     calls the supplied delegate on every timestamp request, while Testably installs
+	///     a fixed-then-mutable <c>MockTimeSystem</c> at construction. The two have no
+	///     observably-equivalent automatic rewrite for arbitrary delegates, and the
+	///     equivalent surface (<c>o =&gt; o.UseTimeSystem(...)</c>) lives in the
+	///     <c>MockFileSystemOptions</c> lambda — a cross-statement fold that conflicts
+	///     with the parameterless / options-ctor fixes when both touch the construction.
+	///     A future sub-phase may add an opt-in fix for the narrow constant-DateTime
+	///     lambda shape with a custom <c>FixAllProvider</c>.
+	/// </summary>
+	public const string MockFileSystemMockTime = "MockFileSystem.MockTime";
+
 	// ── Enumeration properties (Phase 5.1) ────────────────────────────────
 	// These IMockFileDataAccessor properties enumerate the whole mocked file
 	// system. Testably has no direct equivalent — the natural replacements
diff --git a/Source/Testably.Abstractions.Migration.Analyzers/SystemIOAbstractionsAnalyzer.cs b/Source/Testably.Abstractions.Migration.Analyzers/SystemIOAbstractionsAnalyzer.cs
index 63932a5..3b7c129 100644
--- a/Source/Testably.Abstractions.Migration.Analyzers/SystemIOAbstractionsAnalyzer.cs
+++ b/Source/Testably.Abstractions.Migration.Analyzers/SystemIOAbstractionsAnalyzer.cs
@@ -314,6 +314,7 @@ private static bool IsMockFileSystemOptions(IParameterSymbol parameter)
 		"MoveDirectory" => Patterns.AccessorMoveDirectory,
 		"FileExists" => Patterns.AccessorFileExists,
 		"AddDrive" => Patterns.MockFileSystemAddDrive,
+		"MockTime" => Patterns.MockFileSystemMockTime,
 		_ => null,
 	};
 
diff --git a/Tests/Testably.Abstractions.Migration.SystemIOAbstractionsPlayground/ManualReviewTests.cs b/Tests/Testably.Abstractions.Migration.SystemIOAbstractionsPlayground/ManualReviewTests.cs
index 2d268f3..a7f9479 100644
--- a/Tests/Testably.Abstractions.Migration.SystemIOAbstractionsPlayground/ManualReviewTests.cs
+++ b/Tests/Testably.Abstractions.Migration.SystemIOAbstractionsPlayground/ManualReviewTests.cs
@@ -84,6 +84,21 @@ public async Task MockFileData_CopyConstructor_ClonesTextContents()
 		await That(clone.TextContents).IsEqualTo("hello");
 	}
 
+	[Fact]
+	public async Task MockFileSystem_MockTime_ReturnsSelfForFluentChaining()
+	{
+		// TestableIO calls the supplied delegate every time it needs a timestamp.
+		// Testably installs a fixed-then-mutable MockTimeSystem at construction with
+		// no equivalent post-construction fluent API, so this site is reported with
+		// pattern id `MockFileSystem.MockTime` and left for manual migration. The
+		// playground only needs to keep the call shape compiling; the timestamp
+		// semantics of MockTime are out of scope for the parity baseline.
+		MockFileSystem fs = new();
+		MockFileSystem chained = fs.MockTime(() => DateTime.UnixEpoch);
+
+		await That(chained).IsSameAs(fs);
+	}
+
 	private sealed class MyMockFs : MockFileSystem
 	{
 	}
diff --git a/Tests/Testably.Abstractions.Migration.Tests/SystemIOAbstractionsAnalyzerTests.cs b/Tests/Testably.Abstractions.Migration.Tests/SystemIOAbstractionsAnalyzerTests.cs
index 64d965d..48dddb1 100644
--- a/Tests/Testably.Abstractions.Migration.Tests/SystemIOAbstractionsAnalyzerTests.cs
+++ b/Tests/Testably.Abstractions.Migration.Tests/SystemIOAbstractionsAnalyzerTests.cs
@@ -142,6 +142,25 @@ await Verifier.VerifyAnalyzerAsync(
 			Verifier.Diagnostic(Rules.SystemIOAbstractionsRule).WithLocation(0));
 	}
 
+	[Fact]
+	public async Task MockTime_ShouldBeFlagged()
+	{
+		const string source = """
+			using System;
+			using System.IO.Abstractions.TestingHelpers;
+
+			public class C
+			{
+				public void Run(MockFileSystem fs)
+					=> {|#0:fs.MockTime(() => DateTime.UnixEpoch)|};
+			}
+			""";
+
+		await Verifier.VerifyAnalyzerAsync(
+			source,
+			Verifier.Diagnostic(Rules.SystemIOAbstractionsRule).WithLocation(0));
+	}
+
 	[Theory]
 	[InlineData("AllPaths")]
 	[InlineData("AllFiles")]
diff --git a/Tests/Testably.Abstractions.Migration.Tests/SystemIOAbstractionsCodeFixProviderTests.AccessorMethodTests.cs b/Tests/Testably.Abstractions.Migration.Tests/SystemIOAbstractionsCodeFixProviderTests.AccessorMethodTests.cs
index c1d8540..23ec82c 100644
--- a/Tests/Testably.Abstractions.Migration.Tests/SystemIOAbstractionsCodeFixProviderTests.AccessorMethodTests.cs
+++ b/Tests/Testably.Abstractions.Migration.Tests/SystemIOAbstractionsCodeFixProviderTests.AccessorMethodTests.cs
@@ -705,5 +705,38 @@ await Verifier.VerifyCodeFixAsync(
 				Verifier.Diagnostic(Rules.SystemIOAbstractionsRule).WithLocation(0),
 				source);
 		}
+
+		[Theory]
+		[InlineData("() => System.DateTime.UnixEpoch")]
+		[InlineData("() => System.DateTime.Now")]
+		[InlineData("() => System.DateTime.UtcNow")]
+		[InlineData("dateTimeProvider")]
+		public async Task MockTime_HasNoFix(string argument)
+		{
+			// Phase 5.3 ships MockTime as manual review only. TestableIO calls the
+			// supplied delegate every time it needs a timestamp; Testably installs a
+			// fixed-then-mutable MockTimeSystem at construction. The two have no
+			// observably-equivalent automatic rewrite for arbitrary delegates, and the
+			// equivalent surface (`o => o.UseTimeSystem(...)`) lives inside the
+			// MockFileSystemOptions lambda — a cross-statement fold that conflicts
+			// with the parameterless / options-ctor fixes when both touch the same
+			// construction. A future sub-phase may opt-in fix the narrow constant-
+			// DateTime lambda shape with a custom FixAllProvider.
+			string source = $$"""
+				using System;
+				using System.IO.Abstractions.TestingHelpers;
+
+				public class C
+				{
+					public void Run(MockFileSystem fs, Func<DateTime> dateTimeProvider)
+						=> {|#0:fs.MockTime({{argument}})|};
+				}
+				""";
+
+			await Verifier.VerifyCodeFixAsync(
+				source,
+				Verifier.Diagnostic(Rules.SystemIOAbstractionsRule).WithLocation(0),
+				source);
+		}
 	}
 }