1 1/2 hours seems about right. If you go to the steakhouse on board most of the ships they tell you to plan on 2 hours to enjoy the experience. I guess the key to time is table size and how much you get along with the dining partners. I have always felt a little rushed by the waiters in the main dining room. That is why I like the anytime dining versus late or early seating times. The conversation always changes as does the table size.
Happy holidays and cruises to all.