Rhinoplasty is an operation that involves several steps, and removal of the dorsal hump is only one of them. There are a few different ways of doing it, and so the amount of time that it takes to do it depends on which method is used. For example in the open rhinoplasty method the time it takes to expose the dorsal hump is greater, but the time for actual removal is no greater than in the closed method. If the hump is removed as a whole, it might only take a few minutes to do the actual removal. I wouldn't be concerned so much with the amount of time for hump removal as much as the overall result.