I say it's time when it is required by the union, and when there is an alternative other than working such long hours. Here's a "for instance."
On my last show, the AEA contract called for additional compensation during tech week automatically, so the "maximum hours" for the SM don't exactly exist that particular week. But when I was asked to come in on my day off, I made it clear that I would charge those hours as overtime, because if the schedule had been arranged differently I would otherwise be getting a day off. Because the situation could have been avoided (and I was in many other ways being taken advantage of), I felt it necessary to report overtime.
I've also worked in situations where the company really wants to go "by the book," and expects you to report overtime - sometimes they even budget for it. But on the flip side, smaller companies can continue to take advantage of you if you don't report overtime (which is why the rule is there in the first place). In one scenario (not me, but a friend), a green AEA SM was hired who didn't know the rules, and when her more experienced ASM reported overtime, the ASM was told not to report for her scheduled call time, and the newer SM had to pick up the slack. That's a prime example of why overtime is necessary, and a rule.
If the company is in a financial jam, and no one feels abused, then maybe it's a judgement call. But it sounds like this particular company, with two separate teams of SM's, is not hurting financially to be able to compensate you for your work.
Also, I do not believe that our being paid more than the actors has anything to do with overtime - I don't report the extra hours I spend doing paperwork every night into my maximum rehearsal hours - I consider that alone to be enough justification for us being paid more than the actors, and staying longer during tech doesn't even include that same paperwork time, so why shouldn't we be entitled to extra pay?