If you're on the eastern, you'll eat in each restaurant twice, and one (the first one in the rotation) three times. On four of the nights, all three main restaurants have the same menu, on the other three the serve their own menu.
I don't think there's a best or worst night to eat at Palo, as I think it's the best meal on the ship, so we just pick a night and go. But, if you want to have each of the main restaurants' unique menu, I would book on one of the the nights later in the week, as I believe the main restaurants serve their own menus on the first three nights (although this has changed in the past). When you go to book Palo reservations, they'll be able to clarify for you what is happening on which nights in the main restaurants.
On the eastern, I like Tuesday night, so that we can watch the ship leave St. Maarten while we're eating, but over the course of our different cruises, I've eaten there every night but the first, and don't really have a preference.
I hope this helps. Reading over it, I'm confident that it did not.....