What about this:
- Make it 3 weeks.
- Make the server save a demo every X minutes as much as it's capable of (e.g. if the server can hold max 1 hour of demo saving, then it should be something like every 45-50 min)
- Make each demo automatically save itself on a website so at the end of the 3 weeks you can watch every single 45-50 min of the 30240 minute game :DD