For newborns, I find that we get the best success rates when sessions start at 10 or 11 am.  This is because babies don’t tend to sleep all that well at night (which seems like poor planning for everyone involved) and so they are at their sleepiest during the morning.  Sessions that start later can result in a more wakeful baby although of course it isn’t an exact science. The latest session start time that I will take for a newborn is 2.30pm as much later than that, and you are in the baby witching hour of 5pm when they can be very unsettled no matter what you do.