What time would I have to leave the MK (will have a car) to get to DTD for a 1.00 pm ADR at T-Rex?
It depends what you mean by "leave the MK." If you mean exiting at Main Street Station, I would allow AT LEAST a full hour.
After you exit, you need to walk to the Monorail or ferry, wait for a Monorail or ferry, ride the Monorail or ferry to the TTC, walk to the Heroes or Villains tram stop, wait for a tram, ride the tram, walk from the tram stop to your car, drive to DTD, find a place to park, and walk to T-REX.
You can't predict how long your waits will be. For example, if you're parked in the Villains lot but they're now parking cars in the Heroes lot, mid-day trams to the Villains lot could be few and far between.
If you're parked close enough to the TTC not to need a tram, you should be able to save some time.
If your can board a Monorail/ferry and a tram right away and you quickly find a good parking spot DTD, it should take far less than an hour. But you can't rely on such a "bast case" scenario.