Add custom delay to userscript functions.

userscript-function-delay.js

// ==UserScript==
// @name        Delay function
// @namespace   Violentmonkey Scripts
// @include     *://example.com/*
// @run-at      document-start
// @author      Null (r4v10l1)
// ==/UserScript==

// --------------------- Settings ---------------------
var MY_DELAY = 500;             // ms, delayChecker will wait this
var MY_INITIAL_DELAY = 500;     // ms, the script will wait this before the first check
// ----------------------------------------------------

function mainFunction() {
    console.log("This is the main function to be executed.")
}

function delayChecker(customDelay) {
    // Remove after you test the userscript!
    console.log("Entered the checker! You can test the userscript by typing 'condition = true' on the console.");
    if (condition) mainFunction();
    else setTimeout(function () { delayChecker(customDelay); }, customDelay);
}

condition = false;
setTimeout(function () { delayChecker(MY_DELAY); }, MY_INITIAL_DELAY);

You are welcome.