Whether or not you are given leave is the prerogative of your
commander.
If he is feeling generous and wants to give leave, then good for
you.
If he is feeling stingy or you are needed badly in camp, then
too bad for you.
Before you complain, National Service Full-time is exactly what
it is: you are a FULL-TIME soldier.
If you want to do anything else on the side, then your superior
may close one eye, but don't expect him to bend over backwards to
help you.