How long does it take to remove snow from a house roof?

i have 4 guys coming over tomorrow to remove snow from my roof, there not to sure how long it will take them, i have about 3 or more so feet of snow on my roof, were having a bad winter, they said they will be using shovel's and scoops to remove the snow, im just wondering if anyone know roughly how long it takes, i live in a bungalow by the way, thanks