That's so cute!
I've read different opinions on when to make a move. I think it depends on the hen. I've moved them at different times, I even moved one during a hatch, with an egg that was pipped! (because her sister started trying to horn in on the hatch, after all that time of leaving her alone!) The kicker is you don't want her to abandon the eggs. So once you feel she is fully committed, you should be safe to move her. If you do it early on, then you aren't out as much if she abandons them, but the longer you wait, supposedly the more likely it is she will stay with them. So its a tossup!
But in the dark usually does work best, and the sooner after it gets dark, the better, to give her the entire night to settle in and stick with it.
Oh, watch for her to get off the nest and take her "daily dump"... I've found that the more committed they are, the nastier the dump is.

(how's that for a guideline!)
ETA - Pyxis did a pretty nice article here on the subject --
https://www.backyardchickens.com/a/guide-to-letting-broody-hens-hatch-and-raise-chicks