it's not dumb at all!! i never thought about it until i read somewhere else that the "rule" (or is it a suggestion? i guess cuz chickens don't hatch like clockwork..) is that if you begin incubation in the morning/early afternoon it's considered day one, any later than that it's day 0...
i started at 10:30pm at night.... so it was day 0 for me, but then again you just adjust your days by the hour they're set.. so lockdown would begin 18/19 days after you set them at the time that you set them!
i think... i'm about 1/2 way through my first hatch......
It's just an estimate anyway. The rule I follow is if I put them in by noon or before, that day counts as Day One. If it's afternoon or evening, the following day is Day One. Works well.