The head of agency may, on request of an employee serving in a foreign area:
a. at an isolated post performing functions required to be maintained on a substantially continuous basis, grant the employee compensatory time off for an amount of time spent equal to that spent in regularly scheduled overtime work; or
b. at a post in a locality that customarily observes irregular hours of work, or where other special conditions are present, in order to cope with such conditions, grant the employee compensatory time off for an amount of time equal to that spent in regularly scheduled overtime work for use during the pay period in which it is earned.