I moved my chicks out to my coop the day they arrived in the mail back in the beginning of march. generally I prefer keeping the chicks outside, it's been my experience that they fair better, even if it's on the colder side. there is something about being inside that seems to be hard on them. you may be warm enough in your area to use a woolley hen this late in the season, certainly a mother heat pad. I have begun veering away from heat lamps as much as possible, they burn out unexpectedly and are a bit of a fire danger long term.