When they were in Ushuia Chatzos Halaila and Alot Hashachar were the same time...
According to the Alter Rebbe, that's the way it's done in many places.
Even places like London, they follow that system for about 2 months in the summer.
It's not that they're the same time, rather since the sun doesn't go that far below the horizon, so there is no Alos. The AR says we use Chatzos for all things which must end before the night is over.