One simple mechanism would be to run a background thread that check the time once per second and sets a flag if the difference between this time and last time is greater than (say) 2 seconds. This 'worked' for me:

#! perl -slw
use strict;
use threads;
use threads::shared;

my $sem :shared = 0;

async {
    my $last = time;
    while( sleep 1 ) {
        my $now = time;
        if( $now - $last > 2 ) {
            $sem = 1;
        }
        $last = $now;
    }
}->detach;


while( sleep 1 ) {
    print "tum te tum";
    if( $sem ) {
        print "You snoozed me";
        $sem = 0;
    }
}

__END__
C:\test>junk96
tum te tum
tum te tum
tum te tum
tum te tum
tum te tum
tum te tum
tum te tum
tum te tum
tum te tum
You snoozed me
tum te tum
tum te tum
tum te tum
tum te tum
Terminating on signal SIGINT(2)
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