A return permit:
(a) comes into force on the day specified for the purposes of paragraph 15(4)(c); and
(b) remains in force until the earliest of the following occurs:
(i) the period specified for the purposes of paragraph 15(4)(c) ends;
(ii) if the period is varied under subparagraph 17(1)(a)(i)--the end of that period as varied;
(iii) the permit is revoked under paragraph 17(1)(b).