What age can birds start to free range??

[bhg002]

I have 9 10 week old chicks (Possibly 1 roo but not sure yet). They have been confined to their coop and fenced/covered run. I am interested in letting them out to free range at times when I am home just so they have some freedom and can peck at some grass. I do live in a neighborhood on a half acre so I am concerned about them wandering too far. I would love to hear about some similar situations.

At what age can I let them out of the run and they know not to wander too far?
Should I always do it about an hour or so before dark?

 

[dermerchickens]

MIne are 7 weeks and they free-range and we are in between two roads, but they never go near them