Technically speaking it's 20 hrs during semester and 40 hrs during break. Working any hours in excess will put you in work violation and you would be out-of-status. I would strongly recommend do not work more than these hours, just to be on the safe side. Especially since you are planning to work in the college. 

I used to work more than 20 hrs during semester and 40 hrs during summer. I had talked to the DSO and interestingly he charged me couple hundred dollars cash to work more than the specified hours, saying that to work these extra hours I need to have some "immigration" paperworks done. Our DSO got into fraud issues and was fired. People from the main college came to our college and opened all the records of the international student. 

More than half the international student got into immigration violation issues. Me too. I was under the work violation. I realized there was no such immigration paperworks and the USCIS explicitly states that "it's ultimate student responsibility to maintain his/her status", so telling it was DSO fault was no-use. I could have sued the college, but I was not in a position to hire a lawyer or anything.

My fault was I worked in the college and my entire work history was in the record. Off the table, my new DSO told me I would have been better-off if I had (illegaly and silently) worked off-campus for whatever hours, but since they have my work history with "unauthorized hours" I am off-status. I have personally read the USCIS guidelines, and the 40 hrs thingy is pretty much a grey area, it's not clear, so colleges have their own interpretation of the 40 hr cap. Point is, do not take the risk, if your DSO is strict, you might get into trouble.

The main thing here is no employer likes to pay over-time. And the HR would probably be pissed off and get to the international student office with this issue. Then it's your luck.

I got in to a mess. Had to leave the country. Fortunately, I re-applied for visa and was able to come back. However every time I enter the port of entry, I am called for questioning, which is dumb cause after this violation I have traveled three times to nepal and back....

I would suggest don't take risk, and if you are taking it..make sure you have an email or written permission from the DSO and the Human resources.....