I don’t have experience with acupuncture, so I’m mostly commenting to get your thread back to the top and see if anyone else can weigh in.
However, when you couldn’t complete the second interval in your workout yesterday, what were you feeling? Leg fatigue or general/aerobic fatigue? You said your legs didn’t feel sore or heavy when you got on the trainer, but it sounds like they started complaining during that second 20 minute interval. Just to clarify, you’re getting dry needling treatments on your legs, right?
I think you’re right to restructure your training schedule to allow a rest day after your treatment, or perhaps just an easier/shorter workout. At 2 hours and with the length of the intervals within it, Hunter is a tough workout to complete even on a good day. Switching some workouts around might help you stick to your training plan effectively while receiving treatment.