You could probably make the portals any time now. Open them when you are out there to supervise, and make sure they know how to use them to get back to safety. Watch them and the older chickens for signs of aggression. Oh and more fights happen around the food and water stations than anywhere else, so adding an extra one of each isn't a bad idea, either. I'll see if I can find @azygous since she introduced me to the portals and I haven't actually used them yet. All I did was prop their door open a bit so they could fit back into their pen but the Bigs couldn't follow, and I had some hiding places in the run in case the Bigs were between them and "home". My chicks were fully integrated by 4 weeks, so I started a little earlier. Good luck!