Rails for Zombies is a great resource.

The Rails Guides are your holy grails, http://guides.rubyonrails.org/getting_started.html

Read as much of this site on your first day, then go back over it again each day.

A webapp like that is possible to make within a day starting from zero Rails knowledge.

You should at least have some persistence to make it interesting, else you'll be twiddling your thumbs for 6 days ;-) and even then...