I've got the same thing going on. Integrating five 18 wk. old chicks with 3 hens. They've been "together" - but separated by cage, fence, etc - since the chicks were about 10 wks. old. At present the hens are in our large coop and the chicks in a chicken tractor where the hens used to live. The tractor is at one end of the run, the coop is at the other end of the run. We opened them up so that they could co-mingle about a week ago.
When we open the coop and tractor in the morning, the chicks run into the big coop and hang out there much of the day. The hens run to the tractor - attempt to eat all the food from the hanging feeder - and hang out in the tractor most of the day. They just change houses for the day. In the evening, the chicks then go back to the tractor and the hens back to the large coop.
They do hang out together in the run at times during the day. One hen has been very mean to the chicks and the chicks are frightened of all the hens. Lot's of running and chasing going on. There has been pecking and one really nasty "fight" but no blood, thankfully.
If I bring out any treats, I need to put them in about 5 spots as the hens will run to wherever I place the treat and attempt to eat all of it. I'm making sure the chicks get a share of any food but the hens don't make it easy. The hens are also getting FAT as they're trying to eat everything in sight to make sure the chicks don't get it!
I, too, am wondering how long before the hens allow the chicks to be around them without getting run off or pecked.