Document in postgresql.conf that the max_standby_delay default is 30

'seconds'.

src/backend/utils/misc/postgresql.conf.sample

@@ -185,7 +185,7 @@
 # - Hot Standby -
 
 #recovery_connections = on	# allows connections during recovery
-#max_standby_delay = 30		# max acceptable standby lag (s) to allow queries
+#max_standby_delay = 30s	# max acceptable standby lag (s) to allow queries
 				# to complete without conflict; -1 disables
 #vacuum_defer_cleanup_age = 0 # num transactions by which cleanup is deferred