If you don't have a party ticket, you can make your dining reservations till 6:59 on a party night and you'll be OK. You can eat your meal leasurly, and enjoy yourself. But once you leave the restaurant, you have to get outa there! lol
My suggestion is to walk slowly, enjoy the sights, but if you try to participate in anything (like the trick-or-treating or getting on a ride) they will ask to see your wrist band. Once they realize you dont have one, they will escort you to the front gates.
But yeah, to answer your question, as long as your dining reservations are for before 7pm, you be OK.