Peng Lei focused on improving time arithmetic reliability in the microsoft/msquic repository by addressing a subtle bug in the CxPlatTimeDiff32 function. He delivered a fix that ensures correct time difference calculations even when unsigned 32-bit wraparound occurs, particularly for cases where the second timestamp is less than the first. By refactoring the TimeDiff logic in C, Peng reduced conditional complexity and enhanced maintainability, making the codebase more robust across platforms. His work leveraged low-level programming and system programming skills to reduce the risk of timer-related bugs in QUIC flows, resulting in more accurate and reliable timer behavior for msquic.