Start here
Pull them while the centres still look wet
The edge should be set and browned and the middle should look like it needs another two minutes. That is the cue.
Oats absorb water and firm up for as long as the cookie is hot, so the oven is only doing part of the work. If you wait for the centre to look finished, carryover takes it well past finished by the time it cools, and no amount of butter in the recipe will bring it back. This single change fixes more dry oatmeal cookies than every ingredient adjustment put together.
The window: 9 to 13 minutes at 350°F for a normal scoop. Cooks who went to 7 minutes reported a genuinely raw centre; at 22 minutes the cookie is at maximum browning and the chew is gone.
Then this
Leave them on the sheet for fifteen minutes
A hot oatmeal cookie is held together by the oats, and they have not finished setting yet.
Move one straight to a rack and it will sag, tear or come apart in your hand, which is where most “they fall apart” reports come from. The sheet keeps it supported and keeps the carryover going. Fifteen minutes is not fussiness, it is the second half of the bake, and it is also why these are the wrong cookie to rush.
Not the fix
four cooks
Do not bake longer for a crisper edge
Cooks who ran past the stated time reported edges that got duller, not crisper, along with a drier middle.
Crispness in this cookie comes from sugar and from how far it spreads, not from oven minutes. Baking longer to chase a crisp edge costs you the centre and does not buy the edge, which is the worst trade available on this page.
Worth checking
Weigh the flour before you blame the bake
A cup of flour scooped from the bag can hold a third more than a cup spooned in and levelled.
This dish leans on flour less than most, so it is the second thing to check rather than the first, but the effect is the same as everywhere else in baking: extra flour ties up water the oats were going to use. 120 g per cup, on a scale.