Refresh: The refresh interval indicates the time interval at which the secondary server of this zone checks with the master server to see whether its data is up to date. If the data in the master server is the latest, the secondary server will transfer it from the master server. The default is 180 minutes.
Refresh Time - The time, in seconds, a secondary DNS server waits before querying the primary DNS server's SOA record to check for changes. When the refresh time expires, the secondary DNS server requests a copy of the current SOA record from the primary. The primary DNS server complies with this request. The secondary DNS server compares the serial number of the primary DNS server's current SOA record and the serial number in it's own SOA record. If they are different, the secondary DNS server will request a zone transfer from the primary DNS server. The default value is 3,600.