I can't speak to SM specifically but I find you have to be a bit careful with the headliners right 'after' the party fireworks. Wait times will trend down before/during the fireworks, but then there is often a rush to the big ones right after the fireworks (many people have the same idea as you) which can pop wait times for a short period. But generally speaking I've never really seen much of a wait at SM during the times I've glanced at it during any party I've been to (I don't go on SM, full disclosure!).
We did SM at MVMCP at about 10pm and it was a walk on. Assuming crowds and parade/firework times are fairly similar between the 2 ticketed events, I would guess you'll have no issues.
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