TrainerRoad consists of structured plans that start with laying a base, building on it, and then fine tuning your fitness to arrive in peak condition for a goal event. Base is anywhere from 12 to 16 weeks, build is 8 weeks, followed by specialty which is 8 weeks. As such the entire course is 28-32 weeks. There are low, mid, and high volume plans that range from 3 rides at 3.5 hours per week to 5-6 rides at about 9 hours per week. I do low volume as I still ride outside 1-2 days per week during the course of completing the three phases. Ideally if you want to be in top shape for a goal event you just count backward 28-32 weeks before the event and begin the program at that time
The premise is that fitness gains occur as a result of workouts focusing on a percentage of your functional threshold power, or FTP, basically your "hour power" or what your best effort in a one hour time trial would be. Your FTP is tested not by riding all out for an hour but by either an hour long workout in which you do 2 efforts at 8 minutes or one effort at 20 minutes, or by a "ramp test" where power rises 6% percent every minute and you ride until failure. Your FTP is extrapolated from your watts on those efforts and that number guides the remaining workouts in the plan. Endurance rides are maybe 50-70% FTP, and those percentages rise through sub-threshold, threshold, super-threshold, VO2 max, and anaerobic efforts, with the harder workouts left to the build and specialty phases. Plan workouts range from 30 minutes to two hours for the most part. There is no workout shorter than an hour nor longer than 90 minutes in the low volume plan, until the last week of specialty when you taper and the rides are 30-45 minutes.
FTP is re-tested at the end of base, build, and specialty to track your improvements. There is a recovery week every 4th week in the plans to guard against over doing it.
I started what's called Sweet Spot base 1 in mid November, which lasted 6 weeks. I just started Sweet Spot base 2 and a new FTP test showed a quite modest 4 watt improvement. This is my second year with TrainerRoad. I am definitely the fittest I've been in years. I was pretty fit to begin with, so my gains are incremental, but they are there. I'm no longer dropped by some guys who used to drop me, for example (although some guys still do drop me).
When I completed the three phases last year I did all my riding outside. I would do an occasional TR workout on rainy days or if I was time crunched and couldn't get outside. That meant that my rides from late May through mid-November were all outside. Structured training probably isn't everyone's cup of tea. I really like it. I get to make the most of the limited time I have to ride, about 325 hours for 2018.