It appears that the SLA guaranteed uptime for Azure SQL Database is 99.9% or 99.99%, depending on tier. That equates to the following allowable downtime per month (which I think is what they base SLA fulfillment on):

99.9: 43m 49.7s

99.99: 4m 23.0s

Sounds like they need to cough up some money for their four 9s customers...