CustomdarkMode.user.js

// ==UserScript==
// @name         Custom Dark Mode
// @namespace    https://taskinoz.com
// @version      0.1
// @description  A custom dark mode that activates at the times you want
// @author       You
// @match        https://*/*
// @grant        none
// ==/UserScript==

(function () {
    'use strict';

    var active;
    var timeStart = [16, 46]; // 24 Hour Time
    var timeEnd = [16, 47]; // 24 Hour Time
    var now = new Date();
    var sameDay;
    var checkInterval = 0.01; // Minutes
    var x;

    // Customm CSS
    var CSS = `/* Add CSS Here */
        body{
          transition: 0.3s;
          background: #000;
        }
      /* Add CSS Here */`;

    // Check if it spans over one day to the next
    if (timeStart[0] > timeEnd[0]) {
        sameDay = false;
        console.log(false);
    } else {
        sameDay = true;
        console.log(true);
    }

    // Convert to date
    timeStart = new Date(now.getFullYear(), now.getMonth(), now.getDate(), timeStart[0], timeStart[1]);
    timeEnd = new Date(now.getFullYear(), now.getMonth(), now.getDate(), timeEnd[0], timeEnd[1]);
    console.log(timeStart);
    console.log(timeEnd);

    function checkTime() {
        if (sameDay) {
            if (timeEnd < now && timeStart > now) {
                if (active) {
                    removeCSS();
                    console.log("Same - Remove");
                }
            }
            else {
                if (!active){
                    addCSS();
                    console.log("Same - Add");
                }
            }
        }
        else {
            if (timeStart < now && timeEnd < now) {
                if (!active){
                    addCSS();
                    console.log("Not - Add");
                }
            }
            else {
                if (active) {
                    removeCSS();
                    console.log("Not - Remove");
                }
            }
        }
        reCheck();
        console.log("check");
    }

    function reCheck() {
        setTimeout(function () {
            checkTime();
        }, checkInterval * 1000 * 60)
        now = new Date();
        console.log("check:" + now);
    }

    function addCSS() {
        document.getElementsByTagName("body")[0].innerHTML += '<style id="custom-dark-mode">\n/*Dark Mode CSS - Generated by Taskinoz\'s Tampermonkey Extension*/\n' + CSS + '</style>';
        active = true;
    }

    function removeCSS() {
        x = document.getElementById("custom-dark-mode");
        x.parentNode.removeChild(x);
        active = false
    }

    checkTime();

})();