Definitely a job. My workplace actively tries to screw people on overtime. They will get you to work an hour or two over and then the next day make you leave 3 hours early cutting all the overtime you worked off plus some.
Discussion
Any "job" I've ever had has always calculated the hours by the week rather than by the day. Overtime didn't hit until after 40 hours even if I was putting in 15 hour days. I'm sure that varies by company, but you should look at your contract to see how that's laid out.