I also love my group rides, have similar weekly commitments (a Wednesday night worlds/smashfest and a long 3-5 hour weekend ride, plus a propensity to say yes to anybody with any good adventurous cycling plans) and have come at this from a few different angles. No right way or wrong but maybe helpful to share what I’ve tried, what worked well and what didn’t!
Base is pretty easy to figure out. The Low and Medium plans include some higher intensity sessions in SSB2, but I was getting enough intensity work from my outdoor rides and races so went with High Volume, and just picked 3 of the 5 SS sessions each week to get my TSS to the right ballpark, then added in 1-2 easy/recovery rides either indoors and out. Aimed to increase TSS incrementally through the 5 weeks, then an easy week (which I tried to coincide with a weekend race to take advantage of the fresh legs).
Build is trickier. I like General Build as I’m an all-rounder, the workouts are very varied though between threshold, VO2, anaerobic and sprint (plus some tempo and SS sessions in the Medium and High plans). Looking at the sessions I didn’t feel that either of my group rides were a sufficient like for like replacement (the Wednesday ride is a real mix of all intensities), and there wasn’t a clear choice of workout to skip. So ended up trying to accommodate all 3 of the high intensity workouts each week, plus the 2 group rides, plus 1-2 easy/recovery rides. The workouts in the High plan were too tough to make this work, so I dropped down to the Medium ones, even though my TSS is closer to the High plan. Those sessions and my Wednesday ride are also too tough to do on back to back days at the same time (unlike SS sessions), I don’t have the luxury of being able to put 48 hours between those sessions, but have been getting 36 hours recovery by scheduling morning workout followed by an evening one the next day, that’s worked well. The one week my plan got thrown out the window a bit was when there was perfect storm on the weekend ride - higher than usual number of local racers, some strong winds and a hot day, ended up a total hammer fest with breaks and splits all over the place and I had to skip a VO2 session the next day as no way I could have got any benefit out of it. But hey, that’s the fun of group rides, you never quite know how they’re going to play out!