Stress is stress.
The problem is stress quantification from the hikes over 3 days. Personally, I would divide it by two. Then, I would as is my usual case plan on a day by day basis using my estimation of my ability to absorb new load. In practice this means from me.....TSB, HRV, LF/HF ratio, sleep, mood, and hunger to ride. I am guessing the effect of the 5-6 hours of zone 1 based on my experience hiking and riding. Just a guess.....halve the indicated Tss