I find that the "story is too short to even consider starting" crowd normally breaks and starts reading around 30 to 50 chapters in. However, story length is not the only tipping point. You also need to have a star rating above 4 and a number of votes on that poll that is at least similar to your number of chapters. Finally, you also need to already have a certain number of "readers," usually around 300-ish, before you start getting over that tipping point where the band-wagon effect will start up and people will start appreciating your story for it's actual worth.
(I chose my words carefully there, "appreciating your story for it's actual worth." If you've managed to hit all the band-wagon triggering conditions and realize your star rating starts to drop at almost that exact time, well... that's a prime indication that they didn't think much of your story. If you're getting low star ratings before that point though, it doesn't necessarily mean as much. It could just be some of those malicious trolls who like to give people low star ratings just to be mean.)