Cannot set router lifetime to 0 in radvd
In the Web GUI (services_router_advertisements.php), it is not possible to set the router lifetime to 0. The GUI enforces a value of at least 1.
A lifetime to 0, however, is a valid configuration (see, e.g., radvd.conf man page, corresponding option AdvDefaultLifetime). This (special) value means that radvd still advertises the prefix and the operating mode of the network without advertising its own host as a router. Such a configuration can be useful when you have to deal with existing routers or when you run pfsense as a management host in an isolated network.
I've checked 2.3.3-RELEASE-p1 and Version 2.4.0-BETA, build of April 27, 2017. The problem exists in both versions.