I'll admit to being the LACTNUT who is a certified mohel (Conservative
movement).  I suspect that doing the circumcision on the eighth day is less
interfering with the establishment of lactation than doing it at 24 hours of
age.  By the end of the first week of life, the physiologic jaundice has
peaked and should be on its way down and breastfeeding should be pretty well
established, whereas the 24-hour-old baby is just learning how to latch and
suckle.  I don't have any actual data on this, though.
Linda L. Shaw MD FAAP