21.—Where, because of an interruption or cessation of work at F61[his or her] place of employment, existing on the date specified in a notification given under section 12 (3) or 20 or on the date on which an adopting parent is required to return to work under section 12 (2), as the case may be, it is unreasonable to expect an adopting parent to return to work on such date, F61[he or she] may return to work instead when work resumes at the place of employment after the interruption or cessation, or as soon as is reasonably practicable after such resumption.