Missed one.

For the relative enrolment "First day of current month", this could clash with the current time if the current date is the first day of the current month.

What we really want to test in this behat test is the 2 extremes: the user who started a long time ago and doesn't have access any more and the user who started recently, who does have access. To fix all problems with datetime clashes, it's probably better to just use something like 'yesterday' for the current student's enrolment start.