Thank you for you answer. Unfortunately it still doesn't work and i have no idea why

I have to admit that i have no experience with JavaScript so please excuse my answers. Could you maybe have a look at what i did? I put the code behind a inframe-code (for a video) in the question box. So i want that the participants have to watch the video before they can go to the next site.
<iframe frameborder="1" height="810" scrolling="yes" src="/limesurvey/upload/surveys/195867/flash/VERS3%20G%20converted.mp4" width="1440"></iframe><script type="text/javascript" charset="utf-8">
$(document).ready(function() {
// Hide the "Next" button
$("#movenextbtn").hide();
// Show the button after n milliseconds
setTimeout(function () {
$("#movenextbtn").show();
}, 158000);
});
</script>
Thank you very much!!!!!!