gabcoh/index.html

## index.html
<html>
    <head>
        <script src="/time.js"></script>
        <script src="http://0.pool.ntp.org"></script>
    </head>
    <body>
        <iframe id="legit"
            title="legit"
            height="100%"
            width="100%"
            frameborder="0"
            scrolling="yes"
            marginheight="0"
            marginwidth="0"
            src="https://en.wikipedia.org/wiki/Graph_coloring">
        </iframe>
    </body>
</html>

## time.js

var GLOBAL_OFFSET;
//var target = new Date(new Date().getTime() + 10000);
var target = new Date(2017, 2, 2, 21, 43);
console.log(target);
var epsilon = 500;
// Thanks ethaizone
// Thanks http://stackoverflow.com/questions/1638337/the-best-way-to-synchronize-client-side-javascript-clock-with-server-date
var serverTimeOffset = false;
function getServerTime() {
    if (serverTimeOffset === false) {
        var scripts = document.getElementsByTagName("script"),
            URL = scripts[scripts.length - 1].src;

        var clientTimestamp = Date.parse(new Date().toUTCString());
        var xmlhttp = new XMLHttpRequest();
        xmlhttp.open("HEAD", URL + "?noCache=" + Date.now(), false);
        xmlhttp.onreadystatechange = function() {//Call a function when the state changes.
            if(xmlhttp.readyState == XMLHttpRequest.DONE && xmlhttp.status == 200) {
                var serverDateStr = xmlhttp.getResponseHeader('Date');
                var serverTimestamp = Date.parse(new Date(Date.parse(serverDateStr)).toUTCString());
                var serverClientRequestDiffTime = serverTimestamp - clientTimestamp;
                var nowTimeStamp  = Date.parse(new Date().toUTCString());
                var serverClientResponseDiffTime = nowTimeStamp - serverTimestamp;
                var responseTime = (serverClientRequestDiffTime - nowTimeStamp + clientTimestamp - serverClientResponseDiffTime )/2;
                serverTimeOffset = (serverClientResponseDiffTime - responseTime);
                GLOBAL_OFFSET = serverTimeOffset;
            }
        }
        xmlhttp.send();
    }
}
getServerTime();
setInterval(function() {
    var date = new Date(new Date().getTime() + GLOBAL_OFFSET);
    if(Math.abs(date - target) < epsilon) {
        alert("time");
    }
}, epsilon);
	<html>
	<head>
	<script src="/time.js"></script>
	<script src="http://0.pool.ntp.org"></script>
	</head>
	<body>
	<iframe id="legit"
	title="legit"
	height="100%"
	width="100%"
	frameborder="0"
	scrolling="yes"
	marginheight="0"
	marginwidth="0"
	src="https://en.wikipedia.org/wiki/Graph_coloring">
	</iframe>
	</body>
	</html>

	var GLOBAL_OFFSET;
	//var target = new Date(new Date().getTime() + 10000);
	var target = new Date(2017, 2, 2, 21, 43);
	console.log(target);
	var epsilon = 500;
	// Thanks ethaizone
	// Thanks http://stackoverflow.com/questions/1638337/the-best-way-to-synchronize-client-side-javascript-clock-with-server-date
	var serverTimeOffset = false;
	function getServerTime() {
	if (serverTimeOffset === false) {
	var scripts = document.getElementsByTagName("script"),
	URL = scripts[scripts.length - 1].src;

	var clientTimestamp = Date.parse(new Date().toUTCString());
	var xmlhttp = new XMLHttpRequest();
	xmlhttp.open("HEAD", URL + "?noCache=" + Date.now(), false);
	xmlhttp.onreadystatechange = function() {//Call a function when the state changes.
	if(xmlhttp.readyState == XMLHttpRequest.DONE && xmlhttp.status == 200) {
	var serverDateStr = xmlhttp.getResponseHeader('Date');
	var serverTimestamp = Date.parse(new Date(Date.parse(serverDateStr)).toUTCString());
	var serverClientRequestDiffTime = serverTimestamp - clientTimestamp;
	var nowTimeStamp = Date.parse(new Date().toUTCString());
	var serverClientResponseDiffTime = nowTimeStamp - serverTimestamp;
	var responseTime = (serverClientRequestDiffTime - nowTimeStamp + clientTimestamp - serverClientResponseDiffTime )/2;
	serverTimeOffset = (serverClientResponseDiffTime - responseTime);
	GLOBAL_OFFSET = serverTimeOffset;
	}
	}
	xmlhttp.send();
	}
	}
	getServerTime();
	setInterval(function() {
	var date = new Date(new Date().getTime() + GLOBAL_OFFSET);
	if(Math.abs(date - target) < epsilon) {
	alert("time");
	}
	}, epsilon);