For overwater legs like that you can nominate a SARTIME for completion of the crossing, depending on VHF coverage to cancel it at the other end of course.
A problem AMSA have sometimes with the flight note option is the level of knowledge of the reporting person re the specifics of the aircraft and/or details they hold e.g. type,colour, fuel and survival gear carried and the route to be flown etc. etc., hence they put out the advice here under "Lodge a flight note with someone responsible":
https://www.amsa.gov.au/safety-navig...escue/aviation