Maximum range varies per archer. Each bow is different, and each archer is different. This isn't modern mass-produced armaments (though they did mass-produce bows, each one was still made from a different piece of wood with its own quirks), and maximum range also depends on the archer's draw length (how long their arms are) and strength.

One of the stories about Agincourt (that the author didn't mention and I don't know if it's true) is that the French underestimated the range of the English archers and drew up inside their maximum range, so were getting shot before they were ready for it.

So "everyone shoots when the enemy gets into range" would still not be a volley as each archer judges for themself when the enemy is in range.