Even if your temps are spot on they can hatch early. Quail are a bit unpredictable. Lock them down on day 14 and then just wait. 16-18 days is just the average. I wouldn't count them out until day 20 especially if your temps aren't perfect. Make sure to remove any hatched quail within the first day. They need food and waiting sooner than a chicken and they will start picking at hatching chicks if left too long. I ended up with a bald button quail chick because I left the hatched ones in overnight and it was the last to hatch.