Mayweather v Hatton was on at 5am UK time. This will be a fight staged in the UK, prime time for selling. Joshua is also already a bigger PPV star in the UK than Hatton - this fight will comfortably surpass the Hatton v Mayweather figures.
Yes I know, I watched it in a room with about 15 people at the time. About 10 who had almost zero interest in boxing but bought into the hype of the build-up and the two men fighting. "Our Ricky v undefeated loud mouth flashy yank for P4P#1" Joshua & Klitschko is nowhere near as engaging. Joshua isn't as big a star as Hatton was back then and Klitschko certainly isn't a dance partner to match Floyd, especially after his efforts v Fury which is still fresh in the mind. Hearn would bite your hand off for 3/4s of that night I think.