Interesting stuff, links on Twitter are nofollow so to think that you can get indexed let alone rankings is an eye opener.
This is all surface stuff. One you Tweet a link on Twitter, depending on the makeup of your Network (Following/Followers), it could be like sending out 1,000 Link Requests!
I've been testing all sorts of stuff on Twitter for almost two years now. I can tell you that NoFollow is just there for the first part of the equation. Once you Tweet, and the API bots pick it up, that NoFollow get's stripped and away she goes! I know, I've watched it over and over again. My logfiles are a clear sign of what happens immediately after Tweeting a link.
I've had stuff show up in less than a couple of hours depending on time of day, how many people Retweeted, etc. There are all sorts of influences here in the process. Twitter's API is one big pipe of links! And Google love Tweets that are well constructed, use Anchor Text (Custom Named URI Shorts), are Front Loaded, and are Retweeted by quality folks within your network. It's one big happy family of sorts. :)