48 hours is the time require for action I believe, however the claimee can respond in however long they like, but the content must be unavailable until they file a counter claim.
(IANAL)
(IANAL)
As someone who runs a site that hosts content, this is great for us. We aren't allowed any sort of leeway in interpreting the claims and in return we are exposed to no liability. We are simply the middle man and have to do what's asked of us.