GDP = Consumption + Government Expenditure + Investment + Exports - Imports
My cases are:
(1) If the employee is getting paid for his extra-work, his consumption would increase.
(2) This employee might take away the job of someone else --and thus his increase in spending could get nullified
By definition, GDP = the total value of all goods and services produced.
(1) If even after working overtime, the company produces the same amount of goods / service --by definition, GDP hasn't risen at all.