It depends. In general most warning points does not have expiration date. Very few and rare occasions do but I hardly remember on which exactly, possibly for minor offense and applied when some thread gets out of hand temporarily.
However, in general also, your last warning points do expire after the ban expires. For example you need 30 warning points to get banned. If your current points are 20 and you did something inappropriate and get additional 10 points and accumulate total to 30 points, you get banned. After the ban expire, said 10 points will expire and your total warning points will retract to 20.