*** Something like this in Aliases in script editor.

JoinNetStable {
  /timer3 0 360 NotInFBSD-DEV
  /nickserv Identify ....
  /join #FBSD-DEV
}

NotInFBSD-DEV {
  if ($me !ison #FBSD-DEV) {
    /Nickserv identify ....
    /join #FBSD-DEV
  }
}

*** In Perform (mirc options), something like this:
if ($network = NetStable) { JoinNetStable }

.