46 CFR 307.9 - When to report.
(a) Operators required to report under this regulation shall send reports during the Radio Officer's normal duty hours.
(b) Operators shall send reports as follows:
(1) Departure Reports must be sent as soon as practicable upon leaving the Port of Departure.
(2) Position Reports must be sent within twenty-four hours of departure, and subsequently, no less frequently that every forty-eight hours until arrival.
(3) Arrival Reports must be sent immediately prior to or upon arrival at the Port of Destination.
(4) Deviation Reports may be sent at the discretion of the vessel operator. Reports may be sent more frequently than the above schedule, as, for example, in heavy weather or under other adverse conditions.