My family does not eat a TS breakfast, so we usually schedule lunch early (usually around 11:30 am - that's when World Showcase usually starts serving meals). We allow about 90 minutes for lunch.
Dinner tends to be on the late side, between 7:30 pm and 9:30 pm, depending on what else we want to do that day. For example, we tend to aim for the last possible dinner seating at Epcot (assuming we've already seen Illuminations earlier in the trip) so we can spend most of the day in the park and then still have a nice TS dinner. For dinner, we allow about two hours.
The amount of time for a meal largely depends on how busy the resturant is and how many courses you order. We often have an appetizer, entree, and dessert, so TS meals can take a while.