The source code is very readable, and contains all answers in lz-in-base64-encoded JSON. It should be easy to add support for playing previous/future rounds using URL parameters and/or buttons with a userscript.

Edit: it's been compiled with Angular.js, and I don't want to install the IDE to change 8 lines... So I identified the function in the minified version and altered it. When I tell my browser to replace the file with a local copy, the hack works until I load another URL. I'll try to figure out how to keep it pointed to the hacked version (which reads the ?num= URL parameter instead of calculating number of days since the first one) but making a Redirector rule fails because of unexpected content type reported by GitHub (text/plain). I don't want to run my own server, let's see if I can do it another way...

Edit: Done