I don't believe this is legal in the state of illinois. I am a non exempt salary employee. I get paid overtime for any hour worked over 8 hours a day or 40 hours a week. My employer is saying I still have to stay over my 8 hours, but on the following day , I need to leave that much earlier, so as to not accrue or be compensated the overtime pay. They are asking me to do this during the week and also on the weekend. My normal working days are only M-F. Please let me know if this is legal? I think it isn't...
I found this on a lawyer's web site, however, I don't know if it is legit.

“Overtime Pay May Not Be Waived: The overtime requirement may not be waived by agreement between the employer and employees. An agreement that only 8 hours a day or only 40 hours a week will be counted as working time also fails the test of FLSA compliance. An announcement by the employer that no overtime work will be permitted, or that overtime work will not be paid for unless authorized in advance, also will not impair the employee's right to compensation for compensable overtime hours that are worked.”

http://www.workplacelawyer.com/whdsfs23.html