If you are going to the MK after dinner, isn't it just as easy to park at the TTC and then walk or take the resort monorail to the Poly for dinner? No worries about timing then!
If you're running late for dinner, you might consider using the valet parking service at the Poly ($6 plus tip). As far as I know, there is no time limit if you use the valet service.
Enjoy your trip!