Your users computers may have clocks that are not set correctly. ntp.js solves this problem by contacting a known good source of time and calculating the offset from the local machine. This value can then be used to adjust any calculations done based on the current date or time.
The easiest (and recommended, see below) way to use ntp.js for your site or web app is to simply link to the hosted version.
<script src="https://use.ntpjs.org/ntp.js" async defer></script>
The "correct" time is based on the consensus of