Assuming they work 40 hours a week. Do they?

Maybe I’m just off the mark but this doesn’t seem like the kind of job you clock in at 9 and stay till 5.

I would expect much more hours when performing and less when not. I would expect it indeed would be approximately a fulltime job.

it's nowhere close. Most orchestras are playing 1-2 nights a week (max) and each performance has 0 or 1 rehearsal (1 if it's a new program, 0 otherwise). Average when performing is maybe 20hr a week