Changing the TTL of a FQDN address
To make sure that the FQDN resolves to the most recent active server you have been asked to make sure that the FortiGate has not cached the address for any longer than 10 minutes.
There is no field for the cached time-to-live in the web-based manager. It is only configurable in the CLI. Enter the following commands:
config firewall address
set cache-ttl 600