The general rule of thumb for a TS meal is about 90 minutes, but it largely depends on how quickly you're seated, how busy the kitchen is, and how many courses your order. If you were only going to do an entree, then I think you'd make it out. If you were thinking of doing a dessert, then it might be getting pretty close. You could put in the order for everything at once and hope to get things moving quickly. Then remember, after you finish, you still have to find a good place to watch Wishes from (luckily LTT is already near the castle).
If it were me and I wanted to eat a TS dinner and see Wishes, I would allow 2 hours to account for late seating and not having to watch the clock the entire meal.