The maximum period for which any person may be detained in pursuance of any detention order to which the provisions of section 10 do not apply and which has been confirmed under clause (f) of section 9 shall be one year from the date of detention, and the maximum period for which any person may be detained in pursuance of any detention order to which the provisions of section 10 apply and which has been confirmed under clause (f) of section 9, read with sub-section (2) of section 10, shall be two years from the date of detention:
     Provided that nothing contained in this section shall affect the power of appropriate Government in either case to revoke or modify the detention order at any earlier time.