I use a brooder plate in the summer & indoors in the winter. I just got my Mt Healthy chicks yesterday! I would plug in your heat plate the day they are supposed to hatch. Mine shipped at 11:45 the night before their hatch date and were at the post office at 1pm the next day! Called my son to plug it in and get food and water ready, so when I got out of work and grabbed the chicks, the plate would be warmed up. They were lively and friendly.
I let them be for about an hour to warm up and rest, then we took them out for a few minutes to get acquainted to us. Will do that a few times a day for short periods to start. The warmer it is, the longer they can be out of their heat source. You’ll love Orpingtons, they are super friendly.