Will monozygotic twins defecate at the same time if fed at the same time during the first weeks of life?
They should have the same genetics (and epigenetics) since they are monozygotic and the same environment since they live in the same house and they are just born.
I looked if metabolism (assuming it is correlated to defecating) is a genetic trait. I found this review about basal metabolism of infants but it stated that the methods aren't good and not comparable.
If there is no information for humans, what about other mammals?