Not sure about times since it varies depending on park times. However, for a buffet a late lunch is usually a better deal. We ate a late lunch at CP over the weekend and was able to try lunch and dinner items for the lunch price. It was great. Plus, it was pretty slow between the changeover so the restaurant was really quiet. I got to try prime rib and adobo pulled pork for the first time and we're going to go back just for that next time. Well, that and the garlic mashed potatoes.
They are usually somewhat less expensive but the menus are usually somewhat more lunch like. When we went to WDW and were paying for the meals we did always choose to have a late lunch for our TS meals due to the cost being lower. Last week we were on the Free Dining Special, so dinner it was except one day that we couldn't get a dinner reservation where we wanted so we had the late lunch. It depends on the restaruant as to the times. We had a lunch reservation at the Sci Fi for 3:40. Each restaurant was different but had the times posted.
IIRC, most of the TS restaurants start serving lunch around 11:30, and stop by 4:00 (some stop at 3:30; they vary). The menus are similar to the dinner ones in many places. That too can vary. You can check out the different restaurants on the menu site from this board, or on www.allears.com dining.
We like to eat TS meals at lunch. The restaurants seem less crowded and the wait staff less harried.