I'd be really careful, that's a significant size difference. Have they had any time to get used to each other with some sort of barrier between them first? You'll also want something safer than a nest box for them to retreat to, and something they are comfortable in, as the larger birds can easily enter a nest box and then they are just cornered.
I tried integrating at that approx age difference, the younger ones had grown out in a fenced off portion of the run so they saw each other on a daily basis, and I'd even let them have a few supervised "visits" with the bigger birds. Then I tried the night time move. Next morning I went out early to check on them and one of the chicks had basically been scalped from the back of his head to between his shoulder blades. I had left a "safe access" back into their area that only the little chicks could enter, and that was where I found them, but that one chick obviously didn't make it there in time. I waited another month to let him heal and try again, with a little more success that time.