My test to see if a hen is truly broody and deserves eggs to hatch is that she needs to spend two consecutive nights on the nest instead of sleeping in her normal spot. I've had plenty of hens look like they are broody but fail that test.
I've had hens act like they are thinking about going broody for days before they finally kicked over to full broody mode. I've also has some that acted like that for two weeks and never crossed the line. I've also had some that went straight from not broody at all to fully committed.
If a hen is thinking about going broody (the hormones are sort of starting) tossing her out of her nest or disturbing her right at the start seems to discourage her. I leave mine alone for those two consecutive nights before I do anything with them if I want them to go full broody.
Going broody is hormonal. Being broody is instinctive. I brooder-raise and broody-raise chickens. I have not seen any difference in how they act when broody. Either the instinct is there or it is not.