The meeting point is at PIAZZALE GALILEO, FLORENCE in the VIALE GALILEO GALILEI which is 2 kilometers from Piazzale Michelangelo (in front of the entrance to the ParkPalaceHotel).
Apparently the best time to go is during lunch. They are in the parking lot everyday (unless it rains) from 10am until 5pm. The point is to go when the roads are clearer so you don't sit in traffic.