They can start showing sex, but won't go over to flowering until you reduce the light to flowering.
As far as 24 hours of darkness?? perhaps reduced light 12/12? I mean it never goes 24 darkness in the Sun.
I would guess they are just making sure the plant understands now is the time to make flowers and survive.
You ever notice how tiger lillies on the bright side bloom first and those on the dark side take longer?
I mean nature knows when it's time based on light for everything.