For the prelaunching period premium will be charged on the average value at risk during each calendar month or the daily pro rata part thereof for periods of less than one calendar month. For the postlaunching period premium will be charged on the amount insured for the full period. Premiums shall be due and payable within thirty days after receipt by the Assured of notice of the amount thereof and if not paid within that period the insurance shall become null and void and of no effect from the beginning of the period for which the premium charge is made unless the Maritime Administrator agrees otherwise. Payment shall be made to MARAD at the address in §308.2(d), by check payable to the order of “Maritime Administration, Department of Transportation.”