Well, if you're implying as to when your Tamagotchi will have children, it will be when it has a high relationship with another Tamagotchi (4 hearts) and both Tamagotchies are 48 hours after they became adults. Then, if they breed, they will keep the "Tamababies" for 24 hours after having them. (This is without Pausing them. If you pause them, it will be longer. Also, the adults will leave at Midnight after the 24 hours, so it's not exactly 24 hours).
