Why do I always start the game with less time than my opponent?

In bullet this is pretty annoying as I somehow only start with 15 - 25 seconds
You probably are experiencing a lot of lag .
https://support.chess.com/en/articles/8652402-how-can-i-optimize-my-online-chess-performance
https://support.chess.com/en/articles/8584209-how-do-i-fix-my-disconnect-lag-issues
In bullet this is pretty annoying as I somehow only start with 15 - 25 seconds