It depends on the length of the cruise but generally, on a seven-night cruise the first formal night is the second night (usually a sea day) and the other is the night before your last night. It was this way also on the ten-night cruise I was on. On 14-night cruises, you usually will have three formal nights.
We are doing a 7 night Eastern Caribbean cruise. I wasn't sure if they have a set schedule for their differnt theme nights. I do think formal nights are on Sunday and Thursday though. I hope to get more details soon from Princess!
on a 7 day Caribbean cruise you will have 2 formal nights - the first formal - The Captain's Gala Welcome Aboard will be the night of your first FULL DAY AT SEA. Your second formal - The Captain's Final Farewell Party will be on the night of your LAST FULL DAY AT SEA. As for theme nights, the themes are around the food, there will be a French night, Italian night, Caribbean night etc.
LisaK is right, we just sailed to the eastern caribbean, 7 nights. The formal nights were the 2nd night and the last full day. The themes are just for the food and you can ask in the dining room the night before what the theme for the next day will be. We had italian, wild-game, caribbean, etc
Make your reservations for Sabatinis' and Sterling before you get on the ship. They fill up fast. And the formals Mon. and Thurs. when we were on the ship. I remember because my birthday was on Sunday and it wasn't formal.