How did I lose 2 seconds time while premoving?

So we have this hypothetical case: white player has 2 seconds on the clock, and a premove made. But white can still lose on time before his premove is executed? Because of variable lag? And this is all normal? Nobody reacted to my timeseal remark. Don't you think a timeseal mechanism should solve this problem?

@hamstra lichess has said no to timeseals because they can be exploited