under rules for canine agents under subsection (b)(1)(F), or substitution of overtime hours in the same work period under subsection (f)(2)(A), except that no such payment may be made for periods of absence resulting in an hours obligation under paragraph (3) or (4) of subsection (f). (2) Computation The special overtime payment authorized under paragraph (1) shall be computed by multiplying the credited hours by 50 percent of the border patrol agent’s hourly rate of basic pay, rounded to the nearest cent. (3) Limitations The special overtime payment authorized under paragraph (1)— (A) is not considered basic pay for retirement under section 8331(3) or 8401(4) or for any other purpose