I recently had a single chick in an incubator hatch, a couple of days after one of my hens hatched two chicks. My single chick was 2 days old before I gave up on the rest of the eggs. I hate raising a chick alone. so I decided to chance it. When mom hen was settled for the night, I took my single chick down to the coop, messed with mom hen a few minutes and reached under her and got the chicks moving around, slipped mine under her from behind. He nestled right in where it was nice and warm. Not a peep out of him.
Next morning, he was running around with mom and the other two chicks, just like he'd hatched with them. Mom never seemed to know the dif, maybe she thought she hatched another, or maybe a hen can't tell the difference between 2 and 3.
Two other hens hatched some guinea eggs for me, about a week apart. The 1st one I had to find a separate space for, the guineas were attacking her and trying to take the keets. The 2nd one was fighting with a guinea hen over her 4, and one got separated. I gave it to the 1st hen, she took it, no problem. The next day, guinea hen had the other 3, but they'd gotten cold and wet, they could barely move, and I thought they'd die. I took them, warmed them under a heat lamp til they dried and were active again, and gave them to hen #1. So now she has all the keets, a week apart in the 2 groups, she doesn't care. They're all hers.
Go for it, it usually works fine.