In the company I was working for before I decided to change my life considerably, I made 80 unpaid extra hours in one month (240 instead of 160hrs as agreed per contract) which were equivalent to two extra weeks of free work.That's a good advice, @onnovocks. Been there!
They had fired a colleague of mine and I had to do her job on top of mine which was obviously not able within my regular working schedule. As a matter of course, I was totally exhausted after that month and started to make mistakes, which was then their reason to doubt my efficiency.
I would never ever go back to such a system, not even if they paid me 1 million dollar.