Like people said, when they're rushing for World First, they put everything and raid for those hours.
After the race is over and they've the content in farm, it takes them a couple of hours to clear everything (let's say 10 hours).
For the rest of the world, we normally raid 3 hours a day, for 5 days a week, which take us 15 hours each week.
Take your conclusions
PS: I am not counting the endless alt runs they do to equip their 3-4 alts to BiS asap.