About the recruitment time and working conditions of power plants

Power plants are generally recruited at the end of April, May and June (campus recruitment).

Yes, you need a diploma to go through the admission formalities. Those who haven't graduated can only be considered interns.

You can go to the internship with them, but you have to make an agreement with the personnel department of the unit (responsible for recruitment). If you want to take time off to go back to school after finishing your thesis defense (mainly defense), you have to make an appointment in advance and go back to school with your diploma. That's enough. You don't have to wait until after graduation, but your chances of retention will become uncertain. ?