I volunteer with a SAR group. We do most of our training during evenings and weekends. For actual rescue call outs on weekends we can get a good turnout. It is true that during weekdays it is harder, and we get fewer people available. One way it works is if your team grows to a certain "critical mass" of volunteers. That way there are always at least some folks who are free at any given time.
I'm getting older and will probably retire in a couple of years. The good news is that I will have more free time to be available for SAR. The bad news is that I'm not as fast going up the hills as I used to be. That means I will probably not be in the "hasty team", instead I will be in the "old slow guys follow on team".

But I intend to stay involved in whatever way I can, for as long as I can.
My experience is that volunteer SAR teams are overall some of the nicest people you will run into. It is a self selecting group. We all have our quirks, but the real jerks don't seem to hang around very long, once they find out that it is mostly hard work and not much glory.