Unless your hotel has parking "baked into" your rate, then yes, you will have to pay full price for parking. I don't know which hotel you are staying at but most Good Neighbor hotels are well within walking distance to the parks. Almost all of them have about a 10 minute walk.
If you are staying a little further away you might choose to look into a shuttle vs. parking. For those with smaller groups of people it can be much cheaper to use a shuttle than to pay $15 for parking.
To find out the hours of any restaraunt, call 714-781-DINE for assistance.
**EDIT** I see from your signature that you will be staying at the Desert Palms. My advice: walk! You will spend a LOT more time getting through the parking madness (trams, waiting, etc.) than you would if you just walked back and forth. Your hotel is extremely close to the gates. No need to drive.