Parking near the Marketplace can be very tough. We went one Tuesday morning in May and ended up way down near Raglan Road, so it was a bit of a walk to Earl of Sandwich. I am CERTAIN that the majority of those cars were NOT there so their owners could shop (this is the parking lot closest to the buses, after all).
I would drive there rather than take the bus, though, since bus transportation can be an extremely time-consuming task. Plenty of people still use DD to park for free, even though it can add an 60-90 minutes (or more!) each way in travel time to & from the parks. Of course Disney knows this, so I think they make it as inconvenient as possible in order to discourage folks from doing it.
And no, there's no time limit.