Let fallback script use day-old data

In legacy/trac#16907 (moved), Onionoo will be updated to return a 504 error when data is more than 6 hours old. karsten also notes that Onionoo was down for 10 hours doing backups.

If we're updating fallback directories for a release, we don't want to wait for Onionoo. So if there's cached data younger than a day, or if the data is stale and younger than a day, we'll use it.

I'll post a patch to this once I have the number.