((a)) Unless retired or separated on or before the expiration of that period, each warrant officer shall be retired or separated from his armed force not later than 60 days after the date when he becomes 62 years of age, except as provided by .
((b)) The Secretary concerned may defer, for not more than four months, the separation under subsection (a) of any warrant officer if, because of unavoidable circumstances, evaluation of his physical condition and determination of his entitlement to retirement or separation for physical disability require hospitalization or medical observation that cannot be completed before the date when he would otherwise be required to be retired or separated under this section.