Section 18(2)(a) in Rajasthan Civil Services (Pension) Rules, 1996
(a)The authority issuing the order of substantive appointment to a service or post as is referred to in sub rule (1) shall along with such order require in writing the Government servant to exercise the option under that sub rule within three months of the date of issue of such order, or if he is on leave on that day, within three months of his return from leave, whichever is later and also bring to his notice the provisions of clause (b).