You won't know until you board. We haven't recieved our requested dining time either time we cruised. First time we requested 6:15 and got 8:00, second time we also requested 6:15 and got 5:45. We did get the table for 4 (traveling with friends) that we requested. I was surprised about that. We ended up only eating in the dining room 3 times, and our friends 4 times. The dining room and time will be on your sign and sail card.
Carnival legend November 2009
Carnival Glory October 2007
Carnival Elation November 2006
Actually, there is a particular dining room that will do the 8 P.M. seating, however, I'm not sure which one it is! I'd guess that it'll be the aft dining room, but someone who has been aboard "Conquest" will be able to tell you. Hang in there, and one of the great "CruiseMates" will come to the rescue.
I just did a little research, and in April of this year we sailed the "Liberty", a Conquest class ship, and we did indeed have the 8 P.M. seating. We were seated in the Silver Olympian restaurant, ie: the aft restaurant. This tells me that there is a 90% chance that you'll be seated in the Monet Dining Room, ie: the aft dining room, if indeed you do have the 8 P.M. seating. You won't know that for sure until you get your sign-n-sail card. Good Luck!!!