If you want them to stop sitting, itd take a few days to cure. The passive approach is to have the nest box setup with chicken wiring with a gap under it. Then soem hay ontop. Theyll sit and cannot keep heat and will eventually stop being broody.
The active approach, of you want to avoid a bunch of work, is a five gallon bucket of cool water. When you catch them being broody, dunk them into the bucket so theyre wet. Keeps them from being able to incubate and theyll associaite sitting on eggs with a big bucket of cold water. I had one especially broody hen that didnt respknd to the chicken wire trick and i had to use the bucket. Took a week but she finally stopped.
Reasons i stopped mine from sitting is because i have no rooster, so wont have chicks. Id rather her be up and about eating and scratching, than eating little an no laying.
Letting her sit isnt a bad thing. Shell just protect those eggs. If you have cold winters and a coop which will drop get cold, shell prevent them from freezing.