Probably. Mythos doesn't stay open late unless the park stays open until 10pm. And the wait for Mythos really isn't that long.
The best idea is to go there for lunch at 11:30am, and take the left overs back to your room.
The other idea, is to share a single meal, and save room for desert. The Wrap of the Day and Cowboy Burger are good ideas. You get free bread to snack on. You'll be full, and then you can continue touring the park.
From reading reports, the only restaurants you really need reservations for are Emirils, and Tchop Chop.