Something

alias away1 {
  away $$2-
  amsg I am now away for reason $$2-
  set %awaytime. [ $+ [ # ] ] $ctime
}
on *:text:*:#:{
  if ($left($1,1) !isin $me) {
    halt
  }
  elseif ($left($1,1) isin $me) && ($away == $true) {
    notice $nick I am away: $awaymsg and I have been away for $duration($calc($ctime - %awaytime. [ $+ [ # ] ]))
  }
  else {
    halt
  }
}
alias back {
  away
  amsg I am back from away : $awaymsg
}