Go up early and plan to stay awhile if your plan is to watch the fireworks. (You can order food in the lounge). About an hour before the fireworks, here's what usually happens:
Those who are seated already decide to keep their seats until after the fireworks show is over.
Those who are coming in for ADRs during that time aren't being seated because the people at the tables aren't leaving.
The folks waiting for ADRs crowd into the bar/lounge area to wait.
People who ate at Ca. Grill earlier in the evening are also taking advantage of the fact that they can present their receipt and be allowed up to watch the fireworks. If they get there early, they too usually wait in the lounge/bar area.
So it's entirely possible if you don't get there early enough, you won't be able to go up to the lounge unless you have an ADR or a receipt. I don't think you can expect to walk up to the check-in desk fifteen minutes or even a half hour before the start of Wishes and be let up to the lounge. (If you go early you also have a better chance of scoring a coveted window seat. There are several in the lounge.)