hi Newbie,
NS will be the most trying time musically, due to the simple reason that the govt wants to take away ALL your time to serve a set of ideals you most likely don't buy into. Thus it will be no wonder you would get rusty, as jamming and practice time will be cut down drastically.
I suggest you take down notes on each song your band wants to jam before hand? it doesn't have to be in standard notation (i.e. Piano Taogeys), but could be a set of lyrics with markings on when you come in, any solos, stop and start again etc. This i feel will greatly help your ability to memorise parts and sequences to songs.
It'll save you the trouble struggling to remember after a week of being cursed at, "knock-it-downs", and other random acts you'll prob not allow yourself to go through were you not wearing green.
So, i don't know any advice on how you can have more practice time, but hopefully this will help you and your band have a more effective jam session. Skills will no doubt get rusty, but should you memorise the parts, who knows? maybe your songs would sound better stripped down!
cheers,
Joash