Work: 8 hours
Sleep: 8 hours
Draw: 8 hours
That's 24 hours right there and that's not even including driving/walking to work, cooking, eating, shitting and showering.
I suppose you could sleep for 6 hours, but as far as I'm concerned, I need between 7-8 hours of sleep. Still, I manage to get between 3-5 hours a day (not including weekends) of drawing time on work days and draw off and on, on the weekends.