I haven't been doing them for long (a week, 3 sessions) but I think I nailed what works for me last time.

2 sets of 7 intervals. I use the 170% of VO2 power number (VO2 for me is ~375w) because my VO2 is better than my FTP. So I do the 'on' intervals at 630-645. Using the 200% of FTP number often thrown around, I would only do them at 600 right now. Tried that, didn't feel hard enough.

Anyway, it goes like this:
- ride out to dead-end section of road, 15 minutes
- do a couple little efforts to open the legs up a bit. Usually 2-3 80% sprints of about 15s.
- Do the first set, 7 "on" intervals of 20s at 630-645w with 10s rest in between each, staying seated the whole time.
- almost hurl
- rest head on handlebars, try not to crash
- spin around for a good 10 minutes
-do second set, same as first except I do all the "on" intervals standing up this time. I sit down for the 10s recovery.
- ride home at 50w (good thing it's all slightly downhill), eat, stretch

Total ride time is less than an hour. I have 9am class, so I head out at 7:00, home by 8:00, quick shower and then slow ride to school (only about 4 minutes)

I'll do 7 intervals again this week, and will try to do 8 next week.