Here's another option:

use Modern::Perl;

say timeLeft( 14, 30, 00 );

sub timeLeft {
    my ( @time, $nowScs, $thenScs ) = ( localtime(time) )[ 2, 1, 0 ];

    for ( 0 .. 2 ) {
        $nowScs  += $time[ 2 - $_ ] * 60**$_;
        $thenScs += $_[ 2 - $_ ] * 60**$_;
    }

    $thenScs - $nowScs;
}
[download]

Output:

1203
[download]

Interesting to script, but not too readable...

Update: Added @time.