Yep, the 7pm start is pretty firm, but you can show up any time really, however I think there is a cutoff for the buffet though at some point but you should have plenty of time to not have to worry about that

I think the Ricks for sunset then Seastar for dinner is a great idea.
Everyone should see Ricks at least once for the experience but the food and drinks are way overpriced and not good at all so I usually tell folks go early, check it out then leave and go to LTU or Ivans for sunset dinner because it is the same view with less crowds and better food, drinks, prices