In “Titanic 2 Maiden Voyage†you can spend 4 ½ happy hours taking Titanic from Southampton to New York. There are other missions that have similar lengths.
It just depends upon how many ocean environments the creator wants to string together. As each environment is only 15 nautical miles across, it can take a few to cover the whole ocean transit.
It is possible to stretch each ocean environment to as much as 150 nm, but there are very few who really want to spend that much time crossing the ocean.