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Microsoft has recently released hot fix 388724 under MS KB 2687741 which resolves a performance issue when failing over a SQL Server 2012 Availability Group from one replica to another.
The basic jist of the problem is that there was an issue with the inter-node communication within the Windows cluster which caused the AG to take longer than expected to fail over.
If you are having this problem I’d recommend reading this MS KB and getting the hot fix installed on your cluster. As this is just a hot fix and not a service pack (it should be included in Windows 2008 R2 SP2) I’d recommend only installing this if you are having the problem it shows.