Fruiting does not start by itself. The fungus needs a signal that its food is ending and conditions outside are good. The grower gives that signal by changing the room: open or cut the bags, drop the temperature, bring in fresh air, raise humidity and give light.
Oyster pinheads appear about a week after bags are opened and reach full size four to five days later. Button pins come 3 to 4 days after venting and become solid buttons in another 3 to 4 days. Milky pins appear 3 to 5 days after the case run ends.