Worked on stabilizing certificate validation in the dotnet/runtime repository by addressing time zone inconsistencies in X509 verification. Focused on the Linux and OpenSSL integration paths, the developer refactored the interop layer to use UTC-based Unix timestamps, replacing local time calculations and ensuring deterministic behavior across platforms. This involved updating the X509StoreSetVerifyTime method to accept DateTimeOffset and directly forward int64_t values to OpenSSL, while maintaining compatibility with 32-bit ARM systems. Using C and C#, they also expanded test coverage to simulate time zone desynchronization, enabling reliable validation and improving the security and reliability of cryptographic operations.