Hi @Excellentchoice, I hope you are doing well.
The first point I would like to make, is that we do not support custom jQuery plugins from our support desk, so it is good you asked this question in the Need Help pages
If you have any issues with this, here is the place to reach out
Second, I have created a small example site, with the countdown timer plugin implemented, and you can clone that to see how it was made: https://webflow.com/website/jquery-countdown
In the Footer of the site, you put a link to where you have the countdown jQuery script stored. In my case, I used rackspace, but you can use dropbox also.
Also in the Footer, you put the script code needed for the plugin:
<script type="text/javascript">
$("#getting-started")
.countdown("2016/01/01", function(event) {
$(this).text(
event.strftime('%D days %H:%M:%S')
);
});
</script>
You can change the countdown date above in the script code.
In the body of the site, is a div with the ID “getting-started”.
​I hope this helps, cheers, Dave