How's this? You could use the same idea to destroy the $messagebox.

#!/usr/bin/perl
use Tk;
use strict;
my $text = 'Hello World..... How\'s this for fun!!    ';
my $mw = tkinit;
$mw->geometry('+20+20');
$mw->overrideredirect(1);
my $label = $mw->Label(
 -textvariable=>\$text,
  -font=>'courier',
   -bg=>'green',
    -bd=>4,
     -relief=>'ridge'
      )->pack(-fill=>'both');
      $label->bind('<ButtonRelease>',sub{$mw->destroy});
      $mw->repeat(60,[sub{$text=~s/(.)(.*)/$2$1/;}]);
      $mw-> after(5000, [sub{Tk::exit}]); # autoclose in 5000 milisecs
+  
      MainLoop;
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