If you have a settling cage around your bob trap i think i would start training them to come in thru the wires and they get a bit of a look around from there. Are they flying enough to get to the settling cage on their own if you open the bob trap? I would put mine in the cage by hand before feeding and see if they could find their way in - you have to be patient but they will do it. It helps if they are eating on their own. Anyway, after you know they can get in thru the trap, maybe after a week of practice, you can remove the cage and let them explore. My first 3 were almost 2 months old. They just explored the nearby roof and practiced very short flights on the roof itself for at least the first 2 weeks. They are only now this week really taking some good loops around the area but not out of sight for more than a minute or so.
I have removed the settling cage altogether and now even the 4 week olds are free to go. They have been up to the roof but no further. I have observed the some are ready sooner than others.
Hope this helps.