Whether or not they want to let you off at night is up to your
commanders.
If your commanders are strictly by the book, they will not let
you take an outside course.
If your commanders are understanding and generous, they may
close one eye.
Either way, if you are ordered for duty at night, you have
absolutely no right to protest even if it means skipping your
exams.
National Service FULL-TIME is exactly what it sounds like.