I don't think its fair to call non-billable hours "homework". Having non-billable hours is part of running your own business. If you own your own business, you can do your nonbillable hours at any time in the day, including not in normal working hours, but you can also do your billable hours at any time of the day.
It's studying or writing (not billable work) that I must do to achieve a good "grade" (i.e., performance review) and it occurs between 9 and 11 pm -- long after I've left work for the day. That's the textbook definition of homework.
I'm also not the owner or anything of the sort; I'm a mid-level IC with no direct reports.
