That this law is broken often is in no doubt, but all it takes is one complaint to the DOL to set things straight quickly. At the very least, if the core hours are documented, it should be fairly easy to make a case for whatever overtime was worked.
I don't think this is true. And it's irrelevant to my point that there are legit reasons for 8 hour "core hours" windows. That discussion was already irrelevant to the point @jph was making: that communicating team expectations by writing them down, making them explicit, and communicating them is a good idea.
Anyway, I just looked up exemption status, and here's what some lawyers have to say about it. I'm certain that the studio I was working for was not breaking any laws by having 10 hour work days with core hours. The way they accounted for it was a tad surprising / misleading to me, but it was in no way illegal.
'An exempt employee has virtually "no rights at all" under the FLSA overtime rules. About all an exempt employee is entitled to under the FLSA is to receive the full amount of the base salary in any work period during which s/he performs any work (less any permissible deductions). Nothing in the FLSA prohibits an employer from requiring exempt employees to "punch a clock," or work a particular schedule, or "make up" time lost due to absences. Nor does the FLSA limit the amount of work time an employer may require or expect from any employee, on any schedule. ("Mandatory overtime" is not restricted by the FLSA.)'