I am a non-EU student at CBS as well. Though I am particularly very careful about never working more than 20 hours/week but I am concerned, this still might happen to me unknowingly. I have inquired about working hours requirements at different portals but I never get one answer for sure. Some people say that I am suppose to never exceed 20 hours /week even if I work less hours the next week, aiming to not exceed 80 hours a month, I. E. 20 hours requirement is not on average but on exact level. Whereas my employer says that I can work 20 hours on average as long as I don't exceed 80 hours a month. E.g. if I work 21 hours one week and 19 the following week then it is not going to be an issue.
I dont want this to happen to anyone when there is no one to tell us the exact policy.

#1: -  

 You can only work a maximum of 20 hours a week but if you have a good understanding with your employer, you can work less one week and cover it up in the next but you have to record both weeks as 20 hours instead of 21 hours and 19 hours. At least that is what my employer told me.

The 20 hour limit is mentioned on your residence permit letter.