Your question of "time" is interesting. I think Sleepers take very little time at all. A knowledge of my expectations compared to the ADP (for the most part; other factors matter of course) makes it quick to find sleepers. Similarly, since they are usually later in the draft, and I don't want to waste picks, I don't have nearly as much invested in my sleepers - finding one 1 out of 4 (as us mere mortals aim for) or 4 out of 4 (sharks only need apply) provides results and satisfaction.
Identifying busts is a bit more bothersome because being correct on a bust can save your season, but misidentifying one can put you in a hole from which no sleeper can pull you out.
Colin