The Lots never close unless they are full due to capacity. We have parked in a WDW theme park lot multiple times before opening. We often drive overnight to beat traffic. (Again we weren't trying to skip paying it just so happened to work out that way.) Usually signs are up that say proceed to parking. You will absolutely NOT get in trouble for parking if the ticket booths are unmanned if you arrive early in the morning. Consider the free parking a perk for arriving extra extra early. Once we arrived at DHS around 6:00 AM to watch my wife run a race. Another time we arrived at the TTC (MK) lot around 6:30 (for a regular 9AM opening) I expect they will man the booths even earlier for those 6AM openings this fall. In both instances we were resort guests and pass holders, but the signs we encountered explicitly stated booths were closed, proceed to parking.