I have seen several questions lose "close votes" after some time passes if the question doesn't get any new close votes. What is the time limit? I mean, after how much time do the already cast votes get deleted?
After a lot of search found similar question asked in Meta StackOverFlow. Jefff there posted the answer. I am posting the same answer here as it is more than a simplest note.
We now use a form of sliding expiration, so as long as close/reopen votes keep arriving at the rate of at least one every 4 days, they will not expire.
Once the votes do expire, vote aging happens every 24 hours, so you can expect the remaining very old close/reopen votes to expire at the rate of 1 per day after that, unless of course someone casts another close/reopen vote in which case the expiration timer resets to 4 days.
Also, if the question has <= 100 views, no expiration on close (or reopen) votes is done at all.