The best hatcheries, from general consensus are Cackle Hatchery and Murray McMurray, for quality, health and customers service.
Depending how far the hatchery is from you, it will be 2-3 days until they arrive and most hatcheries mail chicks Monday or through to Wednesday. Your po will usually call you but you might want to let them know you're expecting chicks in case they don't. Whenever the big mail truck get to your post office is when you're chicks will get there, usually early morning (6-7) so you don't have to wait around all day. Your po might be willing to hold them until you can get there, most don't mind, since you don't have anyone to pick them up.