My understanding is if you valet at CR, you can leave your car as long as you'd like.
BUT, I would offer this as an alternative... park at TTC (assuming it's open), monorail to CR, breakfast, monorail to TTC, then monorail to EC. Here's why... at the end of the day, in order to get back to your car at CR, you're going to monorail back to TTC, have to change monorails, then monorail all the way around to CR (along with all of the other guests going from EC to GF and CR). If you're parked at TTC, you just get off the monorail and head toward your car.
Or, park at CR, have breakfast, then drive to EC and park there.
I personally would be too worried through the entire day if I self parked at CR and just went to a park. I know people have said they've done it, but I'd still be wondering if my car would be the one the tow, and we wouldn't know until the very end of the night.