Try placing this code wherever you want the start button to appear:
<button type="button" id="startTimer">Start</button>
<span id="timerSpan">You have 30 seconds left.</span>
<style>
#[% QuestionName() %],
.submit_div,
#timerSpan {
display: none;
}
</style>
<script>
$(document).ready(function(){
$('#startTimer').click(function(){
$('#startTimer').prop('disabled', true);
$('#timerSpan, #[% QuestionName() %]').show();
var countdown = 30;
setInterval(function(){
countdown--;
$('#timerSpan').text('You have ' + countdown + ' second' + (countdown != 1 ? 's' : '') + ' left.');
if (!countdown) {
SSI_SubmitMe();
}
}, 1000);
});
})
</script>