I put my 1 week old chicks outside for the first time this past Wednesday, and again on Friday. I have 7 chicks and I put them in a large wire dog cage which I wrapped with chicken wire. Half in the sun, half in the shade. They had a blast exploring in the grass and taking they're first dust baths.
I brought them in when it started to cool down a bit (around 5pm)
I put my chicks outside when they were 2 days old. They are now 4 days old and everyday I let them out to roam the yard. Like everyone else says though, stay out there and keep an eye on them. They normally don't stray too far from you. Whenever I walk around they follow me like you see ducklings following their mother. Its 101F here so I'm not worried about it being to cold and at night its around 80 and they have done fine in their cage. Next week its supposed to be 70's for the high so I will probably take them out alittle for the day and then put the light over them to keep them warm. Just depends on how it feels though.