Just to put this in perspective a bit. I had three publications when I applied, a close friend of mine also had three when he initially applied, and another friend only had 1 when she applied. All of us got one. So, you don't need to have amassed a huge vita prior to applying.
I think having a decent idea (that people easily understand) is important. However, including training experiences that complement your project and are in line with the funding agency are key (e.g., clinical experiences that might give your research some context, considerable advanced stats training, additional coursework related to your research proposal if possible, etc.). Also, having very strong letters and a solid mentor are very important. The funding agency is making an investment in you, not the project (in fact, I think the project is the least important piece of the application).
Regarding the turn-around. I applied in August, got my statement back in early Dec, and had 10 days to get my revision done (if I wanted to make the next submission date). I worked tirelessly for the next 10 days and resubmitted. I started the following August. Everyone I know with an NRSA (n=5) has managed to get their resubmission in on the very next submission cycle. Which generally means a 1 year time frame from submission to funding (although I'm sure this isn't always the case). I would suggest that you submit early as long as you have at least 1 publication (preferably a 1st author). Hopefully by the resubmission you'll have a few more things in the works. Fall of your second year is a good time to submit (I submitted fall of the 3rd year and stayed for a 5th year). If you submit that early, you may want to apply for 3 years (in which case you should have a lot of additional training experiences worked in to justify the 3rd year).
And finally, GOOD LUCK! Writing an F31, regardless of whether or not you get it, is a good experience.
