We leave our 3 out during the day while we are at work, but this is usually only about 3-4 hours at a time (we work different shifts). We also have an electric fence we put up last year after our girsl got out, needless to say, they don't go close to the fence now Both the girls wear collars with our id,rabies & tags, but Angus does not wear a collar, he never has. He's too old to try and jump the fence & he doesn't dig....plus, I can't imagine anyone even trying to come in our yard We always keep our fence locked also.
So I personally don't have a problem with letting your dogs stay out, unless the weather is bad (we leave ours in if it's bad).
I think Roxey was around 4 or 5 months before we left her out with Angus in the yard.