Apologies for the copy/paste:
This is the result of lag -- the long and short of it is that it can't be fixed because it's a product of yours and your opponent's network latency and that's something that will always be a part of the equation.
Basically, your local computer keeps it's own clock and continues to count down after your opponent has actually made his move on his computer but before you've been alerted to this (the time of the delay between these two events varies depending on how bad the latency, or lag). When you finally do get the notification of your opponents move it also comes with the clock time for that move, and if the lag is bad enough, a noticeable correction will be applied to your local clock. It's simply the system making sure the time is applied fairly when there is network latency introducing error.
why while I play against opponents with the same lag as mine (wich is almost to full bar) their time start to go down only a few seconds after thier turn start and after they play they get 1-2 seconds back?? what the heck is going on in here?