(We're going to do a separate post on this in a few days probably, but here's a long story short)
Late October is when we started. Put together a spec doc. At first it was like two pages, we basically said: in order for this to be simple enough, we have to get it down to one page. The goal was simple sharing with your family, no bullshit involved.
Mark got a proof of concept up within 24 hours (layout, basic functionality, database,etc.) From there, we spent the rest of the time tweaking things, testing, user vids,etc.