I live north of Seattle. I just removed the MHP on my Cornish Cross at 4.5 weeks, but they run warm, for regular chicks I usually go to week 5 or 6, all depending on how they behave, and leaving a hutch for them to huddle in would be good... definitely protect from draft. the best way is to gradually lower the temp level on the pad till it's basically hardly doing anything and as long as you are not seeing signs of distress, you should be good about now.