How long does a failover for SQL Server Availability Groups take?
Personal observation from experience with both FCI and AG failovers, with reasonable high volume transactional system (40k trx/sec). For each consider 6 databases ranging in size from 500MB to 4TB in size. Times listed for failover are what it takes for the database to up and in a writeable state on the new node. Your mileage can, and will vary, but this is at least a data point for you.

Cluster failover: 47 seconds (avg)

AG Failover: 10 seconds