That said sartimes are yesterday's technology born out of necessity before full radio coverage,
Oh, where's that?
In any event if you put in a 3hour sartime and ditch half hour into the flight you will be waiting 2.5hrs before they even start enquiring. Useless to you if bobbing around in the sea.
Common Sense says you wouldn't put in a 3 hour SARTIME for an overwater flight, and instead operate on skeds per AIP -