I could be wrong, but if my memory is correct I think overall was intended to be removed from the ranking methods as it doesn't really make sense to use that metric.
looking at the code in sources/rankings.php I notice overall is not included in the array,
$ranking_periods = array('daily', 'weekly', 'monthly');
so it looks like we intended to remove that option from admin settings, I'll confirm with Basti to make sure hopefully his memory is better than mine on this one.
A list that never resets becomes stale very fast, and encourages cheating for new members to catch up.
