Normally, lobster is on the same night as the first formal (at least on CCL it is) but the point I was going to make is that menu's change each night and they can change between cruises, so there may not be a set night.
When I went on the Sovereign of the Seas 4nt last September they didn't serve lobster. Carnival does serve lobster on every cruise even a 3nt. Don't know if you are on the 4 or 5nt but it is possible they won't have lobster on the Enchantment.
Regardless, I agree with dave, I have not been overly impressed with the lobster on the cruises. Having ONLY been on CCL so far (working on changing that....) I can say that the lobster is hit or miss while all the other food on CCL has been very good. The exception is the lobster in the supper club on the Carnival cruises. Its made fresh when you order it unlike the assembly line food you get in the main dinning room. I assume it would be the same for the "extra charge" dinning rooms on a RCCL ship.
I was on the enchantment in march and they did have lobster..it was a 5 night cruise..however it is not the same kind of lobster that we new englanders are used to...they serve "caribbean lobster" which is smaller and tougher...but there are plenty of other wonderful things to have.....going on the enchantment again in two more weeks!!!!!!!!!!!!!!!
we were on the Empress 7 night to Bermuda in July and it was served on Monday night, and our waiter never told us it was lobester night, and if we were running late(we were docked in St. Georges) that we could eat at the Late Dinner.Other waiters told their guests, but ours never did.