Any more than 20 hours and you’ll likely be ripping your hair out. Some people work full-time and go to school full-time, but that’s definitely not the norm. I worked ~6 hours per week - that, along with my EC activities, I had approximately 11 hours of committments per week (it was pretty manageable). Still - it may not seem like much, but those hours add up - and your grades should be your #1 priority.