I know it is hard to believe in Texas, with the warm weather, our minis are growing their thicker winter hair already. We bathed up some of the horses at the farm, and gave them a trim. With the temperatures still in the mid to upper 90s, the horses can get hot when wearing a thick coat.
Bathing, drying, and clipping (full body/face) can take a lot of time per horse. For one horse, this process can take 3-4 hours in all, with the waiting for them to dry. It helps to just get a line of them washed, and started to dry, while someone prepares to clip. Sometimes, if we run out of time, we have to clip the following day, but this is risky, since some of the horses LOVE to roll a LOT.