J.W.
I can only assume you eat lunch in the office so it is a working lunch? Because you only have an eight hour shift.
Anyway in a nutshell you must work four hours and use four hours vacation so you stay till one.
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I would check with your payroll department, not a coworker. I do payroll/HR you would not believe what people do on the say of coworkers and then they go on vacation and we say no, you will not be paid for this. Kind of sucks when your check is short.