[miguendes]

This is a good illustration but I'm not sure if follow your rationale. You said that from 0900-1700 you belong to $COMPANY, contractually.

But if you start working earlier or later, say 1500-2300, that would be fine? As long as you work 8h a day, I assume.

In this case you would belong to $COMPANY from 1500-2300 even though in the contract it says 0900-1700. What happens in this case?

[warrenm]

I'm making the point that unless you can get your schedules to not overlap, you're going to have problems

It's no different than working at a FedEx warehouse from 0000-0500 and then going to drive a school bus from 0600-0900

The hours don't overlap, and the jobs aren't competing

It's at least unethical to be billing time to $COMPANY and $ELSEWHERE for the same clock hours (possibly unlawful in some (many?) jurisdictions)