5 C.F.R. § 848.901 Mentoring.
(a) A phased retiree, other than an employee of the United States Postal Service, must spend at least 20 percent of his or her working hours in mentoring activities as defined by an authorized agency official. For purposes of this section, mentoring need not be limited to mentoring of an employee who is expected to assume the phased retiree's duties when the phased retiree fully retires.
(b) An authorized agency official may waive the requirement under paragraph (a) of this section in the event of an emergency or other unusual circumstances (including active duty in the armed forces) that, in the authorized agency official's discretion, would make it impracticable for a phased retiree to fulfill the mentoring requirement.