here is what one scent company said about it.

BlackDeathScents

I suggest reading it. I learned a thing or two.

well I don’t know when the chemical change takes place but I do know that does come into rut the same time every year and that it’s different for people depending on where they live. In northern Arkansas it begins real close to Nov 3 give or take a day. The does cycles are also on a 28 day period. so if you have a run on Nov 3 you will have lesser ruts on 28 days after and 28 days before (October 7th and  December 1st respectfully).  As a general rule you can expect ruts to take place in the middle of the months but those dates vary from place to place.

As far as using doe in heat scent to soon. yes I do think that if you use it in the wrong part of time you will hurt your chances. I like to put mine out before the rut starts. I try not to put any out if the rut is more than two weeks away.