It doesn’t really make sense why the last hour of any sleep cycle should take the same amount of time as the entire sleep cycle before it. Sleeping from 20:00 to 09:00. From 20:00 to 08:00 takes 10 seconds. from 08:00 to 09:00 takes 10 additional seconds. What’s the rationale for this? Can it just take 11 seconds instead?
You can interrupt your sleep, if you don’t wanna sleep the full hour
It is because when sleeping, the game has to count all behaviour of all NPCs. It is very demanding for CPU and thus slow. So developers sped it up by counting only general behaviour, not every detail. But when Henry wakes up, all the NPCs have to be in correct places with correct behaviour. That is ensured the last hour of sleeping - NPCs start to be fully counted so they catch to the right place of their daily routine. Even if you stop sleep in the middle, the last hour must be counted fully … so it takes some time before you can actually jump to game.
In fact this is far better then it was in beta, when whole sleep was counted in the slow way.
In the beta, if you slept for an entire night you had time for a bathroom break and a quick snack.