I doubt it unless you have a regular park ticket. Since the party doesn't start til 7pm they let everyone slide and come in at 4pm for the most part. Can't you get a later ADR? I certainly wouldn't chance it.
Nope. It will be right at 4:00p when the turnstyles change to accomodate the MNSSHP tickets. You're gaining an extra 3 hours with just that ticket. That should be plenty of time to fit in an ADR.