Need a place to eat and then linger
Yes, there's a crucial difference between eating at a leisurely pace, and lingering after a meal is over.
As srr said, at most mid to high-end restaurants, you can expect to have the table for 1.5-2 hours, especially if you make it clear to your server upfront that you are in no rush, and ask him or her to course and pace things slowly. However, very few restaurants will allow you to linger at the table once you have finished desserts.
My dinners at Incanto in Noe Valley usually last about 2-2.5 hours. But I order multiple courses, and make it clear from the start that we want to take things one or two dishes at a time.