The limit is the amount of time they have built up and then all members gain 2 days per month (one on the 1st and one on the 15th).
There are some instances where site staff could step in but normally that is if a player is trying to prolong a hopelessly lost game:https://support.chess.com/customer/en/portal/articles/1444860-what-is-vacation-abuse-
how long can Sharkwolf's vacation last? Isn't there a vacation time limit? it's been 6 or 7 weeks.