The CERN Staff Rules and Regulations exclude the possibility for students to do overtime, night work, Sunday work, standby duty, shift work, and you are therefore not entitled to compensatory pay or leave.

This does not imply that you can only work from Monday to Friday from 8.30 a.m. to 5.30 p.m. with a break of one hour. However, any additional worked hours may be compensated in agreement with your supervisor by time off during the appointment (and not at the end of the appointment).