The Sperm's Long Journey. A man may ejaculate 40 million to150 million sperm, which start swimming upstream toward the fallopian tubes on their mission to fertilize an egg. Fast-swimming sperm can reach the egg in a half an hour, while others may take days. The sperm can live up to 48-72 hours. Only a few hundred will even come close to the egg, because of the many natural barriers that exist in a woman's body.
9.4 Giving birth. Normal delivery. Children that are born between the 36th and 39th week (38 and 41 weeks after the LMP) are considered as being normal deliveries. Statistically, only 2/3 of all children are born within the 3 weeks around the calculated date of birth and around 80 % within a month around the predicted date of birth.
As has already been mentioned, the pregnancy will last about 35 days, although some will give birth in as few as 30 days and others have been known go as long as 46. Most, however, will have a normal 34 - 36 day pregnancy. If the female does not give birth by her last expected due date, give her at least another 11 days before assuming that the breeding wasn't successful. Your expectant mother will require a nest box at least one week before her first due date.