It would depend on what kind of trees. We had the same thing done recently. I know it's not good for flower beds for nearly a year. It needs to break down and go through a heat. If they were oak trees, those are toxic to chickens. See the chicken treats chart and scroll all the way down to the bottom. There are many links there including one on toxic plants for chickens. Oak trees are on that list. If the trees/stumps you had ground up are not toxic to chickens, I still think it would be better to wait at least 6 months before using them. Just MHO.
Our county dump has a greenwaste recycle program. Every 2-3 months they grind up all the greenwaste into mulch and leave it for the public to pick up for free.
I always go down and get several trash cans full of the mulch and toss it in my run. My girls go wild over it. The mulch is freshly ground up and a mix of anything and everything that was once a plant or tree. So far nothing bad has happened to my hens. It is pretty amazing to see 4 big pile of mulch get thrown about and scattered in search for that one delicious bug at the bottom of the pile. Within a month all the mulch is gone and its back down to dirt. Where the mulch goes I have no idea.
Give your girls the mulch to play with. If you are worried about it being too fresh, then let it sit for a couple months then give it to them, it will have the added benefit of extra bugs and worms in it that your girls will love.