High delay lag between master/slave in Postgres 9.3
In other servers with a lot of traffic the delay is small.


By this statement, I am assuming that this server does not have a lot 
of traffic.

If there are no transactions to replay, then the value of pg_last_xact_replay_timestamp() will not advance merely due to the passage of time.  Also, archive_timeout will only kick in when there is something to archive.  If there is no new WAL data since the last archive switch, then the existing WAL file (which is empty except for the initial header) will not be archived just because 5 minutes have passed.

A possible work around is to set checkpoint_timeout to 300 seconds as well.  In 9.3 with this setting, the checkpoint will create records to be archived, and the archival will create work to be checkpointed, so you will generate a nearly empty file every 5 minutes on an idle server.  Most people consider this to be a bug, but perhaps it is a feature for you.