How far behind is Secondary in AlwaysOn replica ? ( LAG )

Get-AlwaysOn_Availability_Groups_Lag,info.sql

--How far behind is Secondary in AlwaysOn replica ? ( LAG )
--http://blogs.extremeexperts.com/2013/11/04/sql-server-alwayson-how-far-behind-is-secondary/
--"There are a lot of times customers ask me how much time is my secondary behind my primary?
--Such a simple question can be answered easily using some good DMVs."

SELECT AGS.name                       AS AGGroupName, 
       AGL.dns_name			          AS Listener_dns_name, 
       AGL.port				          AS Listener_port, 
       AGL.ip_configuration_string_from_cluster    AS Cluster_IP_addresses, 
       AR.replica_server_name         AS InstanceName, 
       HARS.role_desc, 
       Db_name(DRS.database_id)       AS DBName, 
       DRS.database_id, 
       AR.availability_mode_desc      AS SyncMode, 
       DRS.synchronization_state_desc AS SyncState, 
	   DATEDIFF(MINUTE, DRS.last_redone_time, DRS.last_hardened_time ) AS DELAY_min,
	   DATEDIFF(SECOND, DRS.last_redone_time, DRS.last_hardened_time) AS DELAY_sec,
	   DATEDIFF(MILLISECOND, DRS.last_redone_time, DRS.last_hardened_time) AS DELAY_ms,
	   DRS.redo_queue_size,
	   DRS.log_send_queue_size,        
       DRS.last_hardened_time, 
       DRS.last_redone_time,
	   DRS.last_hardened_lsn,
	   DRS.end_of_log_lsn, 
	   DRS.last_redone_lsn
	   
FROM   sys.dm_hadr_database_replica_states DRS 
LEFT JOIN sys.availability_replicas AR 
ON DRS.replica_id = AR.replica_id 
LEFT JOIN sys.availability_groups AGS 
ON AR.group_id = AGS.group_id 
LEFT JOIN sys.dm_hadr_availability_replica_states HARS ON AR.group_id = HARS.group_id 
AND AR.replica_id = HARS.replica_id
LEFT JOIN sys.availability_group_listeners AGL
on AGL.group_id = AGS.group_id
--WHERE HARS.role_desc = 'PRIMARY'
--WHERE Db_name(DRS.database_id)= 'SomeDbName' 
ORDER  BY AGS.name, 
          AR.replica_server_name, 
          Db_name(DRS.database_id)