I have three broody hens right now.
One, a SF, is not due to hatch for another 10 days or so. So far her eggs look good. Another, a silkie, hatched a single chick (now) 6 days ago. The third, another SF, was due to hatch last night or this morning (not real accurate on the dates, we were gone & DSD didn't mark it down).
I went to the feed store yesterday intending to buy chicks for the SF because I was almost 100% certain her eggs wouldn't hatch. She only had 4 to start with, I had to throw 2 away and the other 2 didn't look good. I got her 5 JG chicks. While I was there, I decided to take a chance and get my silkie some more chicks, to go with her singleton. Kinda risky, since her own chick was 5 days old, but mama is a silkie and her chick is on the smaller side; so I figured I'd risk it.
Got home around 4 PM. Didn't really want to keep the chicks in the house any longer than necessary with our two dogs and two cats; plus I'm not set up for brooding them inside right now. Working as quietly as possible, I went out and slipped the 3 baby polish under my silkie. This was fairly easy. The silkie "Jethro" has been taking care of her single chick, but still in full broody mode - flat as a pancake, waiting for more to hatch even though she doesn't have any more eggs under her. When Jethro stood up and spied the new chicks under her you could positively see the relief on her face. She started singing! She's a happy hen now and taking great care of all of her babies.
I knew the SF would be pretty easy to deal with too. She's easygoing (for a broody). I made a big deal of removing her one egg that I knew was bad and then reached under her with 2 of the five chicks in my hand. Left them. Then reached under her again and added the remaining 3 chicks. She also seemed very relieved to see chicks under her, but wanted her remaining egg back too so I gave it to her. If it still hasn't hatched by tomorrow I'll take it from her while she's out with her chicks. At that time I also moved her and the chicks to a larger dog crate.
So I defied conventional wisdom by working in the daytime and moving one of them, but I had my reasons. I know my hens very well and I knew what they would tolerate and what they wouldn't.
All is well on the farm this morning