If you get Tk to work, this is one way to do it. It draws 360 tagged segements in the background color (so they are invisible, and when the spacebar is pressed, changes their color to black making them visible. It then sets up a repeating, timed callback that makes the segments invisible again one at a time.

#! perl -slw
use strict;
use Time::HiRes qw[ time ];
use Tk::Canvas;

our $TIME ||= 10;

## Fudge factor! using 850 instead of a 1000 works
## reasonably well for timeperiods of 5 to 30 seconds
## on my machine. Adjust to suit processor speed.
my $repeatTime = int( 850 * $TIME / 360 );
print $repeatTime;

my $mw = MainWindow->new;
my $canvas = $mw->Canvas(
    -width => 640,
    -height => 480,
    -bg => 'white',
)->pack;

## Create 360 tagged segments white (invisible).
for my $tag ( 0 .. 359 ) {
    $canvas->createArc(
        80, 0, 560, 480,
        -fill => 'white', -outline => undef,
        -start => $tag + 90, -extent => 1,
        -tag => "t$tag",
    );
}

## Bind action to space bar
$mw->bind( '<space>', sub {
    ## remove previous alphanumeric code
    $canvas->delete( 'code' );
    print time();
    
    ## make circle visible by setting the color of the segments
    $canvas->itemconfigure( "t$_", -fill => 'black' ) for 0 .. 359;
    
    my $tag = 359; ## Start with the first tag to 'remove'.
    my $rep;
    
    ## Set up the repeating callback with the delay calculated earlier
    $rep = $mw->repeat( $repeatTime, sub {
        
        ## if the last segment has been removed
        ## beep, display the code and cancel the timer.
        if( $tag < 0 ) {
            printf "\a";
            $canvas->createText( 300, 240, 
                -text => 'AN ALPHA-NUMERIC CODE', -tag => 'code' 
            );
            $rep->cancel;
            print time();
        }
        ## If a quater of the circle left, beep and change the color t
+o red
        if( $tag == 90 ) {
            printf "\a";
            $canvas->itemconfigure( "t$_", -fill => 'red' ) for 0 .. 9
+0;
        }
        ## make the next segment invisible.        
        $canvas->itemconfigure( "t$tag", -fill => 'white' );
        --$tag; ## Next segment to remove.
    });
});

$mw->MainLoop;
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There is a fudge factor in the timer calculation (using 850 instead of 1000 milliseconds), to account for processing time. 850 workd fairly well for short countdowns (5 to 30 seconds) on my machine, but it will need adjusting to accomodate your processor and graphics card performance.