Add NOTE callout about DateTime calculation limitations in default interface methods tutorial (#47311)

* Initial plan

* Add NOTE callout about DateTime calculation limitations

Co-authored-by: BillWagner <[email protected]>

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: BillWagner <[email protected]>

Author: Copilot

docs/csharp/advanced-topics/interface-implementation/default-interface-methods-versions.md

@@ -47,6 +47,9 @@ First, add the new method to the interface, including the body of the method:
 
 :::code language="csharp" source="./snippets/default-interface-members-versions/finished/customer-relationship/ICustomer.cs" id="SnippetLoyaltyDiscountVersionOne":::
 
+> [!NOTE]
+> The preceding example uses `DateTime.Now.AddYears(-2)` for simplicity in this tutorial. Be aware that `DateTime` calculations can have edge cases with daylight saving time transitions and leap years. For production code, consider using UTC time or more robust date calculation approaches when precision is important.
+
 The library author wrote a first test to check the implementation:
 
 :::code language="csharp" source="./snippets/default-interface-members-versions/finished/customer-relationship/Program.cs" id="SnippetTestDefaultImplementation":::