I think the only time it is officially closed is when they clean them. Usually early morning while most people are eating breakfast or sleeping. I have read of folks being in the pools at all hours and not having anyone tell them to vacate. I know the jacuzzis are used all hours of the night.
It doesn't really close unless they have to clean it. We used the pool each night with no problem. The bar closes early though before dinner. Probably to keep noise down for guests eating at Patois. I wish I stayed open later.
We brought our drinks from the room to the pool at night.