You want to take all day, the idea is to ride fast enough so you can take a decent amount of time at the free food stops and slow enough to enjoy the atmosphere.
Ride the event once and use the other days to explore. The event makes a good start (assuming you are used to Alpine style riding or have at least one day to warm up) or end to a holiday.
reggie – you can ride the circuit anytime, they leave the sign posts up all season. It is worth doing the event for the atmosphere etc.