Maybe. There can be long waits there after you checkin. I'm sure we have waited 30-40 minutes after our ADR time in the past (we don't go there anymore!). If that happens to you, I don't think you will have enough time to eat, transport back to MK and arrive prior to the parade starting. Or it would be close and you might be stuck watching from the train station.
If the parade is important, I would get a reservation time around 5:30 or 6:00, if possible, or schedule one of the activities for a different night.