I've been a few times. I think a good session is 90 minutes. 60 seems too short for me but 90 is good enough to get the full experience. You really have to know how to relax though.
1. Mind racing, everyday worries at hand (~45-60 minutes)
2. Thinking through actual concerns and whats important (~30 mins)
3. Complete relaxation
It's an incredible experience if you devote the time to it, but to really feel it you need to get through the first stage which can take over an hour. I left happier and more peaceful than I had been in some time.
1. Mind wandering (~5-10 minutes)
2. Sleep (~whatever time is left)
What keeps you awake all that time?