We do maintenance for Online Services for Ashes on Tuesday mornings. During this time, I wouldn't expect any online services (match making, leaderboards, etc.) to work. Normally, we are done with it in under 2 hours, but sometimes (though rare!) go over. If they happen to go over, we try to provide status updates on where we are in the maintenance, and how much longer it'll take.
If we do a maintenance (expected or unexpected), we'll be sure to post on the support forums with info on when it'll start, and how long it's expected to last.