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Yes. Overtime is usually determined by the number of hours worked per week, not per day. I had a job with flex time for a few years. It was really convenient. If I needed to leave work to do something I could just make it up another day. If I slept in I could just stay late. Fuck that job was easy, probably too easy.

As an x contractor project manager this is something that's established way before agreeing to the contract.

They need to be aware that certain things happen during planning and implementation of a project.

And if your agreement is 8hr days and you work 14hrs one day because your waiting on delivery of a product or a contractor is held up at another site. That's 2 days of work and you need to account for that in your proposal.

If you dont thats your money not the company your doing the work for.

If you sign up for OT I think you're allowed to leave whenever you want. That's how I see it and how it's done for mine. I'll even show up and say I'm too tired or something and they say it's fine. Which is justified when you already worked 48 hours in 4 days.

No it’s not legal.

Corporate Australia/America/the west needs to be nuked.
You are only allowed to work “reasonable” overtime, check your fairwork or relevant industry relations awards as set by federal govt.
Reasonable can be 1hr OT p/yr.
Many agreements also explicitly state the amount of OT in an ebb or approximate enterprise agreement to be averaged out over the course of 4 weeks.
Honestly just skull fuck to death these corpo cultists, especially HR.

Wha? Legal? If I pay you to rake the leaves in my yard we may or may not agree to the time frame expected.