If they are similar in size then I'd put them together in the morning when you have some time to watch. My roosters all transitioned well into my coops with my hens after they matured enough to mount and crow. My pullets and hens all just ignored him. I would wait until the pullets are at least as big as my cockerel. A smaller cockerel is fine too. Also If at all possible put them in pens where they have a little contact between the wire. I always mix my coops early in the morning so the are a little groggy and then I can watch, I haven't had any issues except the normal pecking order, and a couple bullies that I separate for 5 minutes then put them back.
Hope this helps,