On FGT default VRRP advertisement messages are sent once every second. The frequency can be changed with theadv-intervaloption to change the frequency of sending these messages (1 - 255 seconds). These frequency messages are in seconds.
Theadv-intervalalso affects the period of time that a backup VRRP router waits before assuming the primary router has failed. The waiting period is three times theadv-interval. For example, if theadv-intervalis set to 1, then the backup router waits for up to 3 seconds to receive a VRRP advertisement from the current primary router before taking over the role of the primary router.
I found one article for the active failover using the link-monitor.
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