I know it's hard to get out on the trails (at least for me). I'm lucky if I get in a single track ride once a week--or every other. They aren't that accessible. Road riding can be great for mountain biking. If you can get in a road ride along with your two trail rides, that would be great.

I do a tough 60-90 minute interval road ride once a week and a 120-140 minute medium intensity ride. I also try to ride my bike as much as possible: to pick up the kids, run little errands, etc.