Yes.
Say I have an Equinox oil burner under warranty. GM time is 13.0 hours. No matter how long it takes me, I get paid 13.
Now let's say a couple rusty bolts twist off in the head or something. I will use a separate clock time for "other labor hours" to fix that part.
If it's customer pay, sometimes we have to eat that time, sometimes they get it and are OK with it.
Flip side is some jobs don't pay well for whatever reason and can't be done in that time. I eat that. I screw something up, I eat that...
If I'm not billing hours I'm not getting paid.
If more people got paid like me, I feel it would change things for the better. If you want to scratch out a decent living, one must be efficient and also take care to be sure it's done right. No room for half-assed.