I think that you may be missing the focus of kcott's post. It is the repeat function.

Obviously, you start the progress bar when you are ready.

Example

use Tk;
use Tk::ProgressBar;
my $mw = MainWindow->new();
my $per = 0;
$mw->ProgressBar(-variable=>\$per)->pack;
$mw->Button(-text=>"Go",-command=>\&GoForIt)->pack;
MainLoop;

######### This is the important bit ###########
sub GoForIt {
    $mw->repeat(25=>sub{$per+=10;return if $per>100;;$mw->update;sleep
+(1)})
}
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