My very first session, over 20 years ago, was 2 hours. And that's been my average for most of them since then. I do, however, appreciate 3 hour play times and request these from Mistresses with whom I feel a special rapport.

I just can't fathom trying a one hour session. 2-3 hours gives me enough time to really clear my mind, focus, and "give myself" both to the Mistress and to the experience. It allows her to build the scene up to a crescendo and allows me to gradually drift back to earth.