I would figure that parking should be fairly close to the TTC at that hour (no tram) so allow about 15 minutes from the time you are in a parking space to the monorail platform. (Note at that time neither the Ferry nor the Express train will be running.) You may have as much as a 20 minute wait. The Resort Monorail will be stopping at the Poly and GF entoute, so it will be another 20 minutes until you get off the monorail. And then allow about 15 minutes to get through Security the special gate for people with reservations, and walking to CP. So to be safe for an 8:15 reservation I would think you would need to be at the parking lot entrance no later than 7:00.