It takes maybe an hour, tops, to completely break a bike down to saleable components. Takes longer if you want to reassemble the bike than if you don't.

Generally people also have a more critical eye on whole bikes than for parts IMO. One bad part on a complete bike can easily lose a sale, whereas the good remains can be sold easily. This isn't true for every bike, just those made up from individually desirable components.

Breaking a bike is the easiest route, but not the most noble in the view of serious collectors (not that I'm losing sleep over it, do as you wish of course)