2 weeks is the usual answer from a single mating. It can be up to three weeks, or maybe one week-ish if there's another rooster(s) actively breeding her after the single mating. The sperm get in competition and the older sperm can get pushed out... but they can still be tricky little things..
Oh that explains the chick size difference! If the bigger one is a boy, what would you plan to do with it?
it seems that both chicks might be girls. they both stay with me anyway. jumbo has already become a pet chick, likes to jump on my hands and sit.