Probably late Oct - early Nov, my horse is a Tb so has a fine coat and starts to be rugged up with a rain sheet from beggining of sept so dosen't really get a chance to get too cold! Although my friends new forest will have to be clipped much sooner, just depends on the horse and the amount of work there doing really x
My cob has been done already, I say done but my clippers blew up and so he has a leg and half a face left to-do but never mind, and then my ISH will be done in a month or so when he starts to get wooly, I think it really depends on each horse.