Trying to place shortcode/css/html into an IF conditional statement

Instead of getting all terms, looping over them and then searching your array, you can use the has_termconditinal tag ex:

if( has_term( 'z', 'product_cat',$post->ID ) ) {
    ?>
    <div id="post-timer">
        <p class="timebuy">Time Left To Buy:</p>
        <div id="timer-wrap">
            <?php echo do_shortcode( '[tminus cid ="12" omitweeks="true" days=" " hours=" " minutes=" " seconds=" "/]' ); ?>
        </div><!--end timer-wrap-->
    </div><!--end post-timer-->
    <?php
}