Suppose you have an major naval ship (aircraft carrier or nuclear sub) with a small complement of Jews on board. They're divided by the executive officer to stand watches, same as the rest of the crew, 6 hours each. Some of the Jews will stand different watches than others.
So Friday night happens aboard the ship. Assume sundown occurs during watch A. You're on duty, so you can't say the prayers. During this time watches B and C are awake but not yet on duty, so they probably can. Watch D is most likely asleep.
Do the Jews on the different watches have to rotate their individual clocks so they can observe when they go off-shift, as an extension of observing Shabbat in the desert, where each have to create their own individual time reference out of necessity?
The necessity is this: The Jew on A watch when the three stars normally appear cannot perform the observance because that would be dereliction of duty. So there's a necessity to rotate his clock to another time zone 6 hours hence where the three stars would appear as soon as he went off shift. Watches B and C have no necessity. However, the poor Jew on watch D needs rack time after a full day of work. He would need a 12 hour time zone difference! At least that's how I understand it? Maybe someone understands better.