Most of the time, Audit Trail will contact the Laserfiche server every 5 minutes to ask about new audit data.  While there are active sessions in the Audit Trail Reporter, it will speed up to every 60 seconds for the repositories that users are querying.  Audit Trail is subject to the same factors that can slow down other Laserfiche clients - http-filtering anti-virus, slow routers or firewalls, reverse dns delays, etc - but those shouldn't add up to 20 minutes.