If you get ferals, about 30 days. I got my first homers last winter and have them on nests now. Four eggs hatched and two waiting. Gonna call the guy I got them from and see what he thinks. Even if they still leave here, he's on the way to town.
I used ferals for 20+ yrs with great results. Get them on a nest and they do come back. Otherwise about 30 days. Even then you'll probably lose a few. Have had ferals come back from right at 100mi. Almost a guarenteed deal from 50mi.
Gave a friend 9 feral squabs a couple weeks ago. They were flying and eating/drinking on their own. Bridge of their nose was still pink and he let a couple out that hadn't a clue how to get back. One finally did but the other is living on the roof of his loft. If you can get birds that young, you shouldn't have a problem. The one's I gave himhad never been outside a loft before. Don't put them out, open the bobs and let them come and go a few days on their own. Then every couple of days drop one bob till they are all down.
BTW, use bumpers to train retrieving with. Use birds to train a dog on scent