An agency may pay premium pay under § 550.141 only if that premium pay, over a period appropriate to reflect the full cycle of the employee's duties and the full range of conditions in his position, would be:

(a) More than the premium pay which would otherwise be payable under this subpart for the hours of actual work customarily required in his position, excluding standby time during which he performs no work; and

(b) Less than the premium pay which would otherwise be payable under this subpart for the hours of duty required in his position, including standby time during which he performs no work.