Shouldn't be a long wait for the bus that time of morning, and the trip to DTD is about 15 minutes by bus if it stops at TL, right? It will take 10 minutes to drive it. I guess they could save the 15 minutes back to their resort? But if they are going to spend 10-15 minutes finding parking, that evens out the time. They would also need to get good directions of how to get to DTD from their resort and back to I-4 from DTD if they are driving. I've driven around WDW for the last 7 years now, and still can't get anywhere without my GPS, but maybe that is just me.
Chartle--I have parked in both lots that time of day and had trouble. Sometimes we park at the Marketplace, because that's where we end up after DQ. Sometimes we get there later and look for a spot around DQ. Those are usually easier to find, but it would be a long walk to T-Rex.