74. Every commanding officer shall take care that a person under his command when charged with an offence is not detained in custody for more than forty-eight hours after the committal of such person into custody is reported to him, without the charge being investigated, unless investigation within that period seems to him to be impracticable having due regard to the public service. Every case of a person detained in custody beyond a period of forty-eight hours and the reason therefor shall be reported by the commanding officer to the officer to whom application is to be made to convene a general or district court martial for the trial of the person charged: Provided that in reckoning the period of forty-eight hours all public holidays shall be excluded.