The official 3-Days-1-Novel project page is up. MCM, in the introduction:

I will be working from 6AM on October 6 until 6AM on October 9, minus some sleeping breaks and other life hurdles. In that time, I intend to write 51 chapters, at about 1,500 words each. (…) I would like to remind you that I don’t drink caffeine. When you’re done screaming, please resume.

I’m scared already. For him.