I think it makes sense to have it at the top because it's a great deal of work for something that isn't really mandatory, no matter how much people insist it is.

A perk system and Henchmen -> Companions are things that will add a lot more depth and replayability to the game. The Stronghold at the End of Time isn't mandatory, but it does offer more of a thrill factor and a more tangible reward than a day/night cycle. That's why the day/night cycle has the highest requirements.