Hmm, roles are allocated on ability to do them - part of that is being available when you are needed. However all that anyone needs to do is 27 days a year (14 or 15 of which will be consecutive, on annual camp or course). So all you need to do after that is another 12 days of training, which is actually about 5 weekends, since you nearly always train on a Friday of a weekend too - so 2.5 days a hit. As long as you hit that target then you shouldn't be held back.
I would say that as long as yout TC is aware of it then it shouldn't be an issue. I can't always make the weekends but my TAC know why and they are sympathetic to it. As long as I show my mush from time to time then they are ok about it. Invest what time you can but obviously the more you invest the more you will get back.