I've had integrations take 2 days, and as long as 3 months adding a new rooster. There is no set time as all flocks and situations are different. All you can do is try letting them out when you feel it's time and see how it goes. Never rush it. I generally let them mingle during the day, and round them up at night for a while. When things go smoothly it's nice, but when things go badly it isn't pretty. So take your time, and keep an eye on things. That's my advice.
