Every now and then I'll end up with 20-50 minutes of downtime where
all the computers are working autonomously at the same time.
Okay, do you realize that—for the most part—repairing a computer & just sitting around a computer looks pretty much the same, right? Welcome to everyone’s work day!
The reality of any job is—in most cases—you are not hired to be 100% busy all the time, but rather be there so if something does happen you are ready to act.
That is basically every workplace: You come in, do work, and if the work stops it’s not the end of the world. Take advantage of the slack time to wind down a bit. And if you want to feel productive engage in some kind of pro-active work. Like maybe organizing your notes or review things you have repaired.
But all work days are filled with downtime. Don’t get too hung up on it.