I don't know S&D's policy, but at Disney resorts, day visitors may park in a resort's self-parking lot while they are visiting the resort. Once you leave the resort, you are expected to take your car with you. Time restrictions are sometimes enforced, and the resorts have been known to tow cars that they feel have been there too long. There are generally no time limits on valet parking.
If your friends are planning to valet park at S&D, I'd recommend that they ask if there's any time limit.