This is untested.

!repeat !twitter 1 --> repeat !twitter command every 1 min.
!repeat !twitter off --> turn off !twitter repeating.

Code:
on *:text:!repeat *:#:{
  if $nick !isop # { msg # You are not allowed | return }
  if !$3 { msg # Usage: !repeat !<command name> <time in minute/off> | return }
  if ($3 !isnum || $3 < 1) && $3 != off { msg # <time> must be number greater than 0 or off | return }
  var %t $+(#,.,$2), %text $readini(commands.ini,n,commands,$2)
  if !%text { msg # $2 does not exists. | return }
  if $timer($+(repeat.,%t)) {
    if $3 == off { 
      $+(.timerrepeat.,%t) off 
      msg # $2 turns off.
    }
    else { msg # $2 was already repeating. }   
  } 
  else { 
    if $3 == off { msg # $2 was never started yet. }
    else { 
      $+(.timerrepeat.,%t) 0 $calc($3 * 60) msg # $replace(%text,|,-,$,-,%,-) 
      msg # $2 turns on. Auto repeat in $3 min $+ $iif($3 > 1,s) $+ . 
    }
  } 
}