I just looked at the 'new competitor' tables in Time Crunched, and they don't look too tough, maybe they are really for relatively new riders (?), it's hard to tell how 'new' the competitor is supposed to be, "less than 5 years" is a little vague.
I guess I do ride with quite a bit of structure: no more than 2 days off in a row, no more than 3 days on in a row, shorter harder rides twice a week, longer rides Wed night and Sunday am). It seems like I would have to ride road or trainer to do the intervals in Time Crunched, since my trail loop has several short harder hills, spaced out such that I end up doing hill intervals of a sort every lap, timed to the terrain not the clock.
Like ehigh said, I saw good gains moving up to 4x per week. I figured out I can make a sandwich for a quick lunch and sneak in 2 one hour rides per week on a sort of lunch break. I'm fortunate enough that my work schedule allows that, but it's still very random, I can't say which days I'll be able to ride during the day each week, but I can usually find 2 days to ride. It pays to be creative finding time to ride.
When I first got fairly fast 20 years ago (a few decent Expert finishes), a riding buddy was an Expert racer, chasing him up a 1600' climb on a 27 mile loop a couple of times a week was a good program! Finding other faster riders to ride with can be great, and adds to the fun and motivation.
ehigh; try doing 'backwards situps' (I'm sure there's a proper name for them), lay face down on an exercise ball (under hour hips), with your feet under something heavy (I use the end of the couch), drop your head down to the floor (pause), lift your torso and head as high as you can (pause), repeat. Those seem really good for the lower back.