Mine

on *:TEXT:*brb*:#:{
  if (!$($+(%,gone.,nick),2)) {
    /set $+(%,gone.,nick) $ctime
    /msg $chan $nick has stepped away.
  }
  else { halt }
}

on *:TEXT:*back*:#:{
  if (!$($+(%,gone.,nick),2)) { halt }
  else {
    /msg $chan 12,0<<11,0  $nick  12,0>> was gone for: 12 $duration($calc($ctime - $($+(%,gone.,nick),2)))
    /unset $+(%,gone.,nick) $ctime
  }
}