How often do you have to groom (brush) an Old English Sheepdog?

It depends on the individual dog & their coat & environment. Doubtful you need a hour a day unless you are really slow at grooming or if dog's environment is wooded so stuff is easily getting picked up. I count on at least 10,15 min daily but doing a more thorough brushing/combing weekly. It does take work to maintain that coat & good thorough grooming to prevent tangles/mats.