postgreSQL: streaming replication delay

From the standby DB:

crmmbqt=# select now() - pg_last_xact_replay_timestamp() as replication_delay;
┌───────────────────────┐
│   replication_delay   │
├───────────────────────┤
│ 1 day 05:45:26.277667 │
└───────────────────────┘

or get more details with

crmmbqt=# pg_last_xlog_receive_location(), pg_last_xlog_replay_location(), pg_last_xact_replay_timestamp(), case when pg_last_xlog_receive_location() = pg_last_xlog_replay_location() then 0 else extract(epoch from now() - pg_last_xact_replay_timestamp()) end as replication_delay;