Once you are with your driver, máximum waiting time will be half an hour. If you have a delay in collecting your luggage please activate your phone and contact your driver, or send someone of your party to advise him of the hold up.
Yes, it is possible to book at the last minute. First you must find the driver and providing he has enough vacant seats you must then make an online reservation and payment before boarding the bus.
Booster seats are available free of charge, but they must be reserved in advance in the booking process if it is a private transfer. Car seats not obligatory by Spanish law