We've often gone in February. Weather can be warm or cool. We're from northern New England and regardless it feels like summer to us. Some days we've been the only people at the pool, with lifeguards dressed in warm jackets.
Our experience in Jan is that pools open at 10:00AM and close at either 7 or 8PM and yes, as shared by @Narcoossee11 they will be closed completely if it's too cold.
We traveled in january once and the only people at the pool were the staff members. lol.
It was really weird one time when the employee continued to do the pre-scheduled Trivia Quiz and we walked by as he was reading questions on a microphone to a completely empty pool.