While not tropical, per se, the deck party on our Mexican Riviera cruise was held at one of the small outside pools and the "buffet" was held at about 10 pm and there was practically noone there. (Including me, fast asleep - This report comes to you from my hubby and daughter)
That time (10:00) is a bit on the early side because most of the night owls are still eating dinner. The party usually does not really crank up unti between 10:30 and 11:00. The buffet comes later, usually opening at 11:30.
On "Mexican Riviera" cruises, the party usually has a "Mexican Fiesta" theme. On other itineraires in the tropics, the standard theme is "Island Night."