SQL Server Recovery time is the time it takes for SQL Server to rollback or roll-forward transaction not yet persisted to the database after a service restart. Transactions that are uncommitted are rolled back, and transactions that are committed but not yet persisted are rolled forward.
Depending on the volume of transactions that needs to be handled during recovery, recovery may take a long time to perform. This affects the time it takes for a SQL Server restart. Another example when recovery times become a factor is when a failover is done in a SQL Server cluster.
So how can we know how long the recovery time will be?