I would say 10 hours is a good amount of time to work. 20 hours is doable but really pushing it and you should only do it if you need the money. You will average 5 classes that meet 15 hours a week and then you have to factor in homework (usually another 15 hours) and I would really encourage you to join a club and get involved on your college campus. As a freshman, your workload is not as intense as it will be in later years, so you will have time to have a job. Don't overdo it though. If you feel like it is too much, you can scale it back. It does take some time to get used to the college schedule.