What's a good age to unit chicks & hens

[Dbl T in CO]

Hi All ~

I am new to the chicken world so I am turning to you the "chicken experts" for advice.

I recently adopted 5 beautiful Buff Orpington chicks (dubbed "The Golden Girls") that will be 4 weeks old on July 17th. A neighbor of mine had an aunt pass who had (3) 4 year old white rock hens that she is desperate to find a home for. I'm not opposed to taking them in but need to know what is a good age to merge the 2 groups together. My neighbor can hold them until early to mid fall so I have some time to get a plan in place.

My initial plan was to move "The Golden Girls" into the coop at 6 weeks of age. Would it be better to move them in and allow them to get established and then add the white rocks? That seems to be the most logical in my mind because of the age of the white rocks.

The last thing I want is to have anything happen to "The Golden Girls". They take first priority. But I know lots of you have added birds to your flock so I would like to hear about your experiences and what advice you have on the topic.

Thanks.

Terri