The phrase "to punch a clock" means to physically record the time you start and finish work. It indicates that you follow a strict schedule and are expected to work specific hours each day.
Sentences with «to punch a clock»
It's the juice that keeps flowing whether I decide to read a book or punch the clock at a job. (getrichbrothers.com)
In the corporate world, some people just punch the clock to pay the bills. (entrepreneur.com)
Not having to punch a clock in a physical workplace gives you the freedom to (technically) work from anywhere. (theprofessionalhobo.com)