When I first started in July probably 8-10.5 hours. I had trouble falling asleep and when I was asleep I would wake in the middle of the night due to pressure increases that would rouse me then it would take me some time to fall sleep again so I would compensate for this broken sleep by sleeping earlier and trying to sleep in longer.
Now that I am used to CPAP treatment I usually go anywhere from 6.5-8.5 hours per night.