I'm curious, why for three days? I can't imagine you could accomplish much in three days (at least, I couldn't) since you need to setup your environment, get accesses, familiarize yourself with the release system, etc...
I should have asked for just one day only. It doesn't have to be technical. I think this is an easy way to get rejected (inspired by Jia's rejection therapy), rather than asking in person. I doubt people would give me access to anything important. Nonetheless, if someone decide to let me help, it would be a great experience for me, and one more reason other than my resume to hire me.
When I said 3 days, I meant 3 days only. I think it'll make the founders think about the most important things they need to improve on, which can also be handed to someone with little credibility, kind of similar to the idea of contributing to open source projects.