So there's a method in Discord.js's MessageEmbed class, its called .setTimestamp().

.setTimestamp allows you to add a timestamp on your embed footer. Here's an example:

const {
    MessageEmbed
} = require('discord.js');

const exampleEmbed = new MessageEmbed()
    .setTitle("Example")
    .setTimestamp(); // This is what you need!

Read more about .setTimestamp here: https://discord.js.org/#/docs/main/stable/class/MessageEmbed?scrollTo=setTimestamp

If you want to set the exactly time and day you have to use :

var d = new Date,
    dformat = [d.getMonth()+1,
    d.getDate(),
    d.getFullYear()].join('/')+' '+
    [d.getHours(),
    d.getMinutes(),
    d.getSeconds()].join(':');

You have to set the d in the line you want! If you want to add it in footer you do it like this :

.setFooter(d)