My lab puppy is about 3 months now and we are feeding him four times a day (8am, 1pm, 5pm, 8pm) as per Vet recommendation. We are having trouble figuring out when he needs to poop. Most of the times he poop in the morning after food and then in the late evening,which is very convenient to us. But sometimes he poops afternoon and late night and sometimes early morning at 4 !

How can I make him poop only in the morning after food and late evening?