Traditionally, classes start at 15 minutes past the hour.
The following definition of the academic quarter is given in Svensk Uppslagsbok, Vol A – Apostat, 1947: ‘the 1/4 of an hour that passes after the appointed hour before lectures and the like start at Swedish universities, as a matter of tradition.’
Precisely when this practice originated is impossible to determine. However, it is no doubt a result of the fact that the students did not have their own pocket watches. But in the old university towns of Uppsala and Lund virtually all students lived in the vicinity of the cathedral. When they heard its bells ring eight times, for example, it was time to leave home and still make it to the lecture.
In Uppsala, longer than anyone can remember, it has been simply assumed that students and teachers will factor in the academic quarter. This 15 minutes is deeply rooted in academic tradition at Uppsala University.