The nighttime is the time to attempt this, but I would keep checking on this chick under the broody to see if she is taking care of it. And I would be out in the coop before daylight to watch for any aggressive behavior. The broody might take her back with no problem, but could push her out to get hurt by others, get chilled, and she may peck her to death. Just be aware that it can happen. I might be tempted to try it during the day if I could spend a lot of time out with them. You could try it today, and if there is any rough treatment, I would remove her.