All work in excess of the regular eight (8) hour workday shall be overtime and shall be compensated at the rate of time and one-half (1 ½) of the employee's regular rate of pay, except in cases where the employee is required to double back when changing shift, in which case the employee may be required to report back on the same day and is not entitled to overtime pay for such doubling back. When an employee is required to report back to work at a time not contiguous to his regularly scheduled eight (8) hour workday, he shall be guaranteed a minimum of four (4) hours pay at the overtime rate.