I don't really have a good grasp as to how to efficiently force the program to check every x seconds?
......
It turns out that $mw->after(1000, \&sub); works.. then just add that into the sub to repeat..

Hi, Tk::after is usually used for a one-shot delay. What you want is Tk::repeat. Try

my $repeater = $mw->repeat(1000, \&sub); 
.... 
$repeater->cancel;  # when you want to stop it
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and you will not need to repeatedly call Tk::after in your sub.

Here is a basic example:

#!/usr/bin/perl
use Tk;
use warnings;
use strict;

my $mw = MainWindow->new(title => "Timer");
my $elapsed_sec = 0;
my $elapsed_sec_label = $mw->Label(-textvariable => \$elapsed_sec)->pa
+ck();

my $repeater; # declare first so it can be accessed in the callback
    
$mw->Button(-text => "reset", 
     -command => sub {
               $elapsed_sec = 0;
               &repeater();
             })->pack();

$mw->Button(-text => "exit", 
     -command => sub { exit })->pack();

# start first run
&repeater();
               
MainLoop;


sub repeater{

#this is repeated every second, and you can put your is_playing here
$repeater = $mw->repeat(1000 => sub {

               $elapsed_sec ++;
               
               if ($elapsed_sec > 4){ $repeater->cancel }
               
               }  ); 
      
}
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