My chapter was a colony when I joined. I was in the first pledge class coming from a formal recruitment, and we got our charter and were initiated that fall. The colony had been organized in the fall of 1999, I believe, and we were chartered in October of 2000. So it took about a year.
As for being overexcited, don't be afraid to show that you're really interested! Unless you're scary about it (i.e. raving about how you've already painted your entire house pink and green and have adopted a family of turtles), I think you should be fine. So don't worry!
I'm not sure about the recommendation, though, since this is a little different than formal recruitment...I'd say it couldn't hurt, but could anyone else help us out here?