For us, usually a bit more then 90 mins, honestly- but we're almost always doing three courses at signature restaurants. Two courses at an in-park restaurant may go faster to some degree (eating at the Plaza versus eating at Shulas, for instance, you'd probably be adding at least 20 minutes if not more on to meal at Shula's even if you did do three courses at both).
Some places simply just take longer: if you want steak well done, or if you want a pizza at Via Napoili. If the food is already prepared, it'll take a lot less time. Getting a cupcake from the cart at BoG or getting an ice cream scoop anywhere is faster then waiting for them to pour fifteen sauces on a cake somewhere, probably.
...And this all requires your waitperson not to randomly wander off somewhere after you're done with the entree but before you order dessert/get your check, which they are prone to doing.