High Availability - HA Timer
HA Timer settings define the time for exchanging packets such as Hello and Heartbeat packets, also set the times for the HA pair devices before taking an action such as remaining active as in monitor fail hold up time and so on. Recommended settings are preset for most general fail overs. The other options are 'Aggressive; that helps in faster failover and 'Advanced' where custom settings can be made. Unless we are very sure what settings is needed the best would be Recommended.