Any state officer or employee not covered by Part 2.6 (commencing with Section 19815) of Division 5 when working overtime at his or her headquarters on state business may receive his or her actual and necessary expenses, during his or her regular workweek, subject to rules and regulations adopted by the Department of General Services limiting the amount of the expenses and prescribing the conditions under which the expenses may be paid. However, each state agency may determine the necessity for and limit these expenses of its employees in a manner that does not conflict with and is within the limitations prescribed by the Department of General Services.