I set my eggs about 6.30 in the morning, my bators will get them to temp buy noon or so, and I do count today as day 1. But if I set at 6 or 7 tonight. I would count tommorow as day 1. I don't think it really matters. It depends how fast your bator is going to get your eggs to temp. If it takes 15 to 20 hrs to get your eggs to temp, then tommorrow would be day 1. If you get the eggs to temp in 4 or 5 hrs. then today can be day 1. The eggs will start deveoplement when they get the right temp, so it kinda depends on when your eggs get to temp as to when inncubation begins.I added 17 eggs this morning to a bator that had 16 eggs in it. That was at 7.00 am My temp has recovered and stabilzed at 99.5 at by10. so today is day 1 for them.