When I started planning for this it was going to be 5 days a week, 8 hours a day. I moderated that to four days a week 6 to 8 hours per day by the time I actually started because I didn't want to burn out on it. Now it's more like 8 to 10 hours a day 6 days per week. I don't think burnout is in the cards at this point, but I'm still trying to moderate it and take time to do other things.
Like reading about writing, and studying writing, and researching publishers, and, and, and... I guess it's getting out of hand. But I do have plenty of time for my other hobbies, so it's not too bad.