You'll want the temps to be between 70-85 degrees F to bring them outside, watch out for surfaces like blacktop though, that can be in the 100s in the sun, that you don't set them down on a super hot surface.
As to whether you should bring an individual snake out, that depends on the snake and how confident you are in handling one. The little babies are very quick and can be difficult to grab. So I'd suggest waiting until they are bigger, if you are unsure about handling them. If you do take a baby out (works for adults too but especially for babies) set them down in the middle of a wide open space, with no cracks, crannies, fencing or heavy vegetation that they can dart into and be difficult to catch them again. And bringing out a tote or some other kind of cage to put them in if needed is a good idea too.