Hi Lamplite - in 3+0 you don't gain any time. Even the fastest possible (premoving) reduces time by 0.1s each move. You can test this yourself by looking at the times for moves after games.
Getting extra time in 3+0 blitz?!


I’m playing blitz and my opponent is running low on time, they’re premoving everything but are getting .1 extra seconds almost each move. Is this normal, or some kind of bug?
It's lag compensation and/or small disconnects
https://support.chess.com/article/423-why-did-the-clock-times-suddenly-change-the-clocks-seem-broken

In blitz, you can't gain time so it is probably a bug or a glitch
Clocks still count down while waiting for the move from the opponent but the time from server to the receiving client doesn't count against the moving player's clock. So the clocks will get adjusted some on every move, regardless. In time trouble and higher lag situations, it will be very noticeable.
I’m playing blitz and my opponent is running low on time, they’re premoving everything but are getting .1 extra seconds almost each move. Is this normal, or some kind of bug?