Anyone have success doing 90 minute overunder workouts the day after a threshold session? Looking at the plans, I don’t see any back to back. I am thinking about this due to timing over the next few days. I would rather take care of the intense work before a Saturday long endurance group ride than doing the over unders on Sunday after Saturday’s ride. I don’t want to compromise the quality of the workout or risk bailing either way, so looking for the best option. Or am I overthinking this?
It depends 
In a perfect world, us regular joes could complete every workout exact how Coach Chad lays it out. Unfortunately, we sometimes have to make compromises when life gets in the way. Right or wrong, I personally usually err on the side of getting the work in however I can.
I’ve done hard workouts back-to-back on occasion (or even back-to-back-to-back…don’t tell Coach Chad). When I’ve done it, I make sure (a) I’m super-duper on top of my nutrition (both during the ride and post-ride for recovery), (b) I’m not carrying an excessive amount of fatigue into the block and (c) I’ll have an adequate amount of time to rest in the days following a big training block like that.
Another option would be to consider the 75 minute or 60 minute version of the overunder workout instead. You’ll get some quality training time on those energy systems, but will be less taxing and leave your fresher for your group ride.
I do it whenever I have the two back to back on the schedule. I ride M/W/F/S or Low volume + 1 ez ride on W
Mon VO2, Wed ez, Friday as planned, Saturday as planned.
I have had usually as good or better compliance on the Saturday rides, maybe because Friday is a high calorie day so after the initial warm up I’m feeling fine and ready to go.
Thanks for the responses. After a bad week last week, I just didn’t want to set up myself for failure.