Is it permissible to stay up late at night and sleep until late in the day, knowing that university attendance during the day is regular?

If sleeping does not lead to missing prayers or performing them outside their prescribed times, such that you wake up and pray on time, and then return to sleep, there is no sin upon you. However, if sleeping leads to missing prayers, or combining them, or performing them after their time, then this is not permissible, and you are obligated to repent.