pfSense » pfSense Docs

Suggestion would be:

Minimum & Maximum RA interval
The router sends router advertisements on each interface configured to transmit messages. The advertisements include route information and indicate to network hosts that the router is operational. The router sends these unsolicited multicast router advertisements periodically, with a time range defined by minimum and maximum values in seconds. The maximum interval for sending RA messages should be less than or equal to the router lifetime in RA messages.

Router lifetime
The lifetime associated with the default router in seconds. A value of 0 indicates that the router is not a default router and that associated default routes should be discarded. The default is 3 * Maximim RA interval seconds.