Comment 1 for bug 381741

Isn't that what the hysteresis setting is supposed to regulate?
If the fans turned down immediately after you drop below a certain temperature, your machine would soon heat up again and the fan would repeatedly spin up and down after the temperature dropped again, which is annoying to many people.
That's why let it run for some time after the temperature has gone below the threshhold.
If you want to reduce this time, set a lower hysteresis value in your profile.

Hope this answer helps ;)