In how many days will my milk supply come in?

2 days. Milk supply will increase to meet demand in about 48 hours. This includes after birth, and for the inevitable, normal "growth spurts" when junior decides she needs more. More-frequent (no necessarily longer) nursing for 2 days will increase supply or help your milk "come in.".
1 days. I dislike the phrase "come in." it makes it seem as if there's no milk there at birth. There is! it's just a different recipe, called colostrum. The baby's stomach can only handle a tsp or 2 in the first few days, so that volume you make is perfect. Increase in milk volume happens when its needed, around days 3-5, but can be effected by mode of delivery (c-sections), diabetes and other factors.
1-10 days. Your pre milk or colostrum is probably already in, but your full milk supply can take a few days or more especially for the first time mom. A baby's cry, suckling, and holding your baby are all stimulants to your milk "letdown". Other factors which may help with your milk release is good hydration, good eating habits, drugs and sleep. Supplementation with formula can help in the meantime.