it took me just over half and hour to clip mine , doing traceclips, on a horse thats lives out 24/7 so a fair old coat on him! although this was dependant on him standing like a rock!
but then it does depend on the blades and the horse...
Trace clip took me an hour on my 15.2 thick coated Section D/cob, using Liveryman Harmony clippers. Clearing up in a brisk wind and then getting all the hair out of my underwear later on took most of the day.