Answer this: Why is the clock wrong???
I have complained to support about this but they don't get it. If you are close to the servers you have an advantage. Even premoving you can lose 5 seconds if they are in the US. Support are in the US so they don't see it.
Support staff are all over the world, not just in the US.
The site has code to compensate for some lag but if a member is seeing a lot of it not all will be forgiven. There are some things that can be done client side to minimize connection issues.
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
I have a fibre to the home Internet. Very fast. It is not my end however I see time disappear from my clock even with premoves.
There is a ghost in the code.