How you spend your out-of-class time is your own business, as long as you get your class work and research done. Faculty don't need to know about your job. Also be aware that other students might gossip or tell faculty about your job. Be selective in telling others about your employment.
A big part of success in graduate school, aside from academics, is developing and maintaining good relationships with students and faculty. Put in face time - let others in the department see you.
Choose your job carefully. You don't want your work hours to conflict with school. Many students find that night jobs fit their needs. Also choose a job that is not particularly demanding - ideally one that permits you to do school work. For example, one student worked the overnight shift in a residential treatment center, which permitted her to read. Another option is to choose a job that pays well and requires few hours. For example, a student worked 2 evenings a week as a bartender at a busy bar. Those two nights left him exhausted, but allowed him to spend the rest of the week studying.
Manage Your Time
When your hours are tightly scheduled between class and work, it's very important that you manage your remaining time well. Employ time management strategies, including the use of a calendar and to-do list.
Remember Your Priorities
Sure you need to make money to eat, but remember your ultimate goal: a graduate degree. Attending class and conducting your research must be your first priority. Sometimes that may mean taking time off from work, working fewer hours, or even taking out loans to reduce your need to work. Think about where you want to be in 3 years, 5 years, and 10 years. Sacrifice and debt may be worth it depending on the length of time to graduation and your post-graduation job prospects.