I don't know. If I were exploring this, I would use a bogus student, watch the logstore table as I made changes to my timezone.
As you describe this problem, it does make me wonder if a student, trying to be clever, attempts to change their timezone to give themselves more quiz time. In this case, perhaps they went the wrong way?
I would investigate the logstore entries for this one student to see what else they were doing around the quiz time.
select * from mdl_logstore_standard_log
where userid = (you fill in the student's id)
order by timecreated desc
As you describe this problem, it does make me wonder if a student, trying to be clever, attempts to change their timezone to give themselves more quiz time. In this case, perhaps they went the wrong way?
I would investigate the logstore entries for this one student to see what else they were doing around the quiz time.
select * from mdl_logstore_standard_log
where userid = (you fill in the student's id)
order by timecreated desc