Any state employee, except an employee who has been designated managerial, who is assigned, by the employee’s appointing authority, duties and responsibilities of a job classification higher than the class in which the employee is placed, which assignment has been approved by the Commissioner of Administrative Services, and who works in such assignment on a continuous basis for a period of more than sixty working days, shall be compensated for such time in excess of sixty days at a rate in the higher class which shall not be less than one step in that class above the employee’s existing rate of pay. Service in a higher classification under this section shall not constitute permanent status in such class.