Make sure fallback directories aren't running buggy versions / can deliver a recent consensus
After #20499 (moved), we should reject fallback directories that deliver a consensus outdated by more than N hours, where N is one of [1, 2, 3].
After #20499 (moved), we should reject fallback directories that deliver a consensus outdated by more than N hours, where N is one of [1, 2, 3].