Skipping it because sitting on the trainer for 1-1.5 hrs of endurance is boring = probably a bad habit
Skipping it because you’re cooked from Thursday’s workout, and want to nail the weekend = probably a good idea.
The endurance ride on Friday isn’t going to make or break your plan, but it does add value. So, if you’re sole reason for bailing is that it’s too boring, you’re probably leaving something on the table. If your legs are cooked, or you just need a mental break after a tough week, it’s better to sacrifice the Friday ride than muscle through it and not be recovered for the weekend workouts.
That shouldn’t be the norm, though, and if it is, you may consider reducing volume M-Th, or just removing the Friday ride every week to avoid decision fatigue/guilt of skipping, etc. Then if you’re feeling good one Friday you can add it in, instead of taking it out. Changes the perspective on it!