azure sql failover duration
As Igor Pagliai(MSFT) Blog Here of July 3, 2014 has as very well mention about
Deep Dive: SQL Server AlwaysOn Availability Groups and Cross-Region Virtual Networks in Azure.


SQL Server AlwaysOn Availability Groups Supported between Microsoft
Azure Regions Here
VNet-to-VNet: Connecting Virtual Networks in Azure across Different
    Regions Here
Configure AlwaysOn Availability Groups in Azure VM (GUI) Here
Configure an ILB listener for AlwaysOn Availability Groups in Azure Here


As per Igor Pagliai , Azure Virtual Network Bandwidth and Latency is main factor in failover scenario. 

This is always my primary concern, even on-premise, When I have to build a multi-site AlwaysOn consideration: the connectivity between different datacenters will provide enough network bandwidth and low latency? Remember that we are in Azure and the connectivity between datacenters is provided by connecting two (at least) Virtual Networks using a VPN tunnel that comes with capacity limits, then let me recap some basic considerations:  


Today, for each Virtual Network, you can have only one VPN Gateway;
Each VPN Gateway is able to provide, at the very maximum, a
theoretical limit of 100Mbits/sec;
If you connect a VPN Gateway to    multiple Virtual Networks,
including on-premise local networks, each    channel will share the
same theoretical bandwidth limit of    100Mbits/sec;
VPN Gateway is backed up by two “hidden” Azure VMs of a    certain
size in active-passive configuration, able to provide 99,90%
availability SLA:


Cloud Services, Virtual Machines and Virtual Network SLA
Here

ExpressRoute or Virtual Network VPN – What’s right for me?
Here

NOTE: In this blog post, I will not cover ExpressRoute, I didn’t test for AlwaysOn AG scenarios.