Chapter 9 High Availability for FortiOS 5.0 : VRRP : Configuring VRRP : Optional VRRP configuration settings
  
Optional VRRP configuration settings
In addition to the basic configuration settings, you can change to the VRRP configuration to:
Adjust the virtual router advertisement message interval between 1 and 255 seconds using the adv-interval option.
Adjust the startup time using the start-time option. The default start time is 3 seconds and the range is 1 to 255 seconds. The start time is the maximum time that the backup unit waits between receiving advertisement messages from the master unit. If the backup unit does not receive an advertisement message during this time it assumes the master has failed and becomes the new master unit. In some cases the advertisement messages may be delayed. For example, some switches with spanning tree enabled may delay some of the advertisement message packets. If you find that backup units are attempting to become master units without the master unit failing, you can extend the start time to make sure the backup units wait long enough for the advertisement messages.
Enable or disable individual virtual router configurations using the status option. Normally virtual router configurations are enabled but you can temporarily disable one if its not required.
Enable or disable preempt mode using the preempt option. In preempt mode a higher priority backup unit can preempt a lower priority master unit. This can happen if a master has failed, a backup unit has become the master unit, and the failed master is restarted. Since the restarted unit will have a higher priority, if preempt mode is enabled the restarted unit will replace the current master unit. Preempt mode is enabled by default.
Monitor the route to a destination IP address using the vrdst option.