My date format:
- Today at 12:00
- Yesterday at 12:00
- 01.01.18 12:00
- on 01.01.18 12:00

The code I'm using:

Code:

$(function() {
    var x = $('.timez');
    for (i = 0; i < x.length; i++) {
        x[i].innerHTML = x[i].innerHTML.replace('on', '')
    };
    (function(g) {
        function e(a) {
            var c = (new Date).getHours();
            a = parseInt(((new Date).getTime() - (new Date(a)).getTime()) / 6E4);
            var b = parseInt(a / 60);
            if (0 === b) return a + " minute ago";
            if (b <= c) return b + " second ago";
            if (b > c && b < c + 24) return b + " hours ago";
            if (b > c + 24) return parseInt((b - c) / 24) + 1 + " day ago"
        }
        g(".timez").text(function() {
            var a = this.textContent.trim();
            if (/^(Yester|To)day\sat\s\d{1,2}:\d{2,2}$/.test(a)) {
                var c = a.match(/\s(\d{1,2})\:(\d{2,2})$/),
                    b = new Date,
                    d = new Date(b),
                    f = function(a) {
                        var b = a.getDate(),
                            d = a.getMonth();
                        a = a.getFullYear();
                        return e(new Date(a, d, b, c[1], c[2]))
                    };
                d.setDate(b.getDate() - 1);
                return -1 !== a.indexOf("Today") ? f(b) : f(d)
            }
            if (/^\d{2,2}\.\d{2,2}\.\d{2,2}\s\d{1,2}:\d{2,2}$/.test(a)) return a = a.split(/\W/), a = new Date("20" + a[2], parseInt(a[1], 10) - 1, a[0], a[3], a[4]), e(a)
        })
    })(jQuery);
});

I need to add week, month and years ago. Please help me, thanks.

Please help me

If I understood, you are trying to set a custom date format using the one already displayed in the forum, am I right?
The problem is every user can set their preferred date format in the profile, so your code would not work in all them, only in the one you had...
Also I don't see the reason to do that, there are many date formats available in the profile.

To change it go to Profile  Preferences  Date format

Sorry if I misunderstood, please explain better what you are trying to accomplish.