Your female dog will allow male dog to mate during second stage of heat cycle. First stage is characterized by vaginal swelling and bleeding and this stage can last for 7-10 days. After this, bleeding is stopped or reduced and dogs show a special behavior called flagging which is indication that she is ready for mating. So, your dog will go for mating after 12-15 days of start of heat periods or immediately after cessation of blood.
All dogs are in heat for 21 days the 1st 7 they are just bleeding but can't get pregnant, from day 7 to 14 she is dropping eggs daily and this is when she will conceive, then from day 14/15 she is done with the urge but still is bleeding but it gets less and less. And if she has been bred she will deliver 63 days from the first time the 2 dogs mated thus you get a runt in ea litter for that is the last dog conceived so it wasnt in the womb developing as long as say the first one was, fyi just like us she can go over or under 63 days but that is a safe time frame,and normally the female will get milk in about 24hrs before she whelps