I didn't check Lpfix5's code to see if I could find why it's not working, but instead I wrote (and tested) this
Code:
 menu channel,nicklist {
  Kick Idlers : idle.kick $network $chan
  Set Allowed Idle Time : idle.time $network $chan
}
alias idle.time {
  set %idle $$?="Allowed idle time in minutes or mm:ss format"
  set $+(%,idle.time.,$1,.,$2) $iif($chr(58) isin %idle,$duration(%idle),$calc(%idle * 60))
}
alias -l idle.kick {
  set %chan $2
  if !$+(%,idle.time.,$1,.,$2) {
    idle.time $1 $2
  }
  var %a = 1
  while %a <= $nick($2,0) {
    if $nick($2,%a).idle > $($+(%,idle.time.,$1,.,$2),2) {
      .ban -ku $2 $nick($2,%a) No idling in $2
    }
    inc %a
  }
}