It works like this:

!time 200

Then a timer will start counting down from 200 till 0. When the timer reaches 0 you will receive a message that your timer reached zero.

on *:playend: {
  .remove count.txt
  .msg %x The countdown has reached zero!
  .enable #countdown
}
#countdown on
on *:text:$($strip(!time *)):#: {
  if (!%f) { inc -u3 %f
    if (($2 > 0) && ($2 > 1)) {
      if ($2 !isnum) {
        .msg # * Error: !time NumberHere $&
          (must be followed by a number!)
      }
      else {
        $iif(!%x,set -e %x #)
        var %c $regsubex($str(.,$2),/./g,$+($chr(32),\n)))
        tokenize 32 $sorttok(%c,32,nr) | .disable #countdown
        .msg %x $1 | write count.txt $* | .play %x count.txt 2000
      }
    }
    else { .msg # * The number must be bigger than 0 and 1! }
  }
}
#countdown end