I agree with richmo to enough of a degree not to dispute anything in the above post

The Hotel Plaza Boulevard properties are Official Walt Disney World hotels; while you don't get all the advantages of staying onsite, it would seem reasonable they'd adjust the shuttle schedule for the hard-ticket events.
A couple of alternatives: Call the Hilton and ask the same question. It's the same bus and you might get someone more knowledgeable. Or, hybrid transportation - yes, walk over to the Contemporary, but instead of getting a cab, take the bus to Downtown Disney. The HPB shuttle to/from Downtown Disney WILL be operating - see the schedule in your hotel (lobby, probably) late enough.