Is it permissible for a university student to delay prayer because its time conflicts with lectures, leading to missing congregational prayer, or is it obligatory for him to leave the lecture and go to prayer in the nearby mosque?

Congregational prayer is obligatory and is not waived except for a legitimate excuse. If you can combine attending the congregational prayer and the lesson, then do so. If you cannot, then attend the lesson and then pray in congregation with your colleagues inside or outside the university. If this is not possible and you would be harmed by attending the congregation and missing the lecture, then there is no harm in you praying alone after you finish your lesson, if it is within the prayer time. The fear of harm is an excuse that permits abstaining from congregational prayer.