Carnival Overnight in Havana question

Will be overnight in Havana in August, wondering if there is a time limit on when we should be back on board on the first day? Or is it ok to stay out very late before heading in for the night? Will we be allowed on/off at any time during the stay or only during certain hours? TIA!

As long as you are on board what ever time they tell you before sailing from Cuba the next day, then you will be fine. We were just there on this ship in October.