Countdown to certain date and adding x hours - php

Question

Timer Main
$curDate = date("Y-m-d H:i:s", strtotime("-8 hours"));
$timecountdownend = strtotime($curDate) + strtotime("+1 hours");
$timecountdownstart = strtotime("-8 hour");
$timeleft = $timecountdownend - $timecountdownstart;
if (isset($_POST['type']) && $_POST['type'] == "timerupdate") {
echo $timeleft;
}
?>
Timer Update 5 Seconds
$(document).ready(function(){
var timerText = $("[timer]");
setInterval(function(){
$.post("timer.php", {type: "timerupdate"}, function(data){
timerText.html("Time Left:" + data + " seconds timer.")
});
}, 5000);
});
WHAT ARE YOU TRYING TO ACHIEVE?
The idea is when a user reserves an item, expiration date is set into the database so that the USER that reserved the item cannot hold it forever. So for example:
User A: Reserve Item A.
[SERVER] $database->insert("reservation", $curDate);
[SERVER] 2016-04-03 16:00:00 (After 30 minutes this item is expired)
That what's supposed to happen in the back-end.
WHAT HAVE YOU TRIED?
I've done tons of googling to see how I could add x hours or minutes to the current date and pass that on to become a unix timestamp.
WHAT IS YOUR PROBLEM?
Whenever I try the code above it works but doesn't come up with the right output I need. Specifically the problem is at $timecountdownend = strtotime($curDate) + strtotime("+1 hours");
** NEW **
date_default_timezone_get("America/New York");
$curDate = date("Y-m-d H:i:s", strtotime("-8 hours"));
$date = new DateTime($curDate);
date_add($date, date_interval_create_from_date_string('2 hour'));
$timecountdownend = strtotime($date->format('Y-m-d H:i:s'));
$timecountdownstart = strtotime("-8 hour");
$timeleft = $timecountdownend - $timecountdownstart;
if (isset($_POST['type']) && $_POST['type'] == "timerupdate") {
echo $timeleft;
}
OUTPUT: 7200 seconds (STUCK though). It's precise but it's not counting down.

Answer 1

Did you consider http://php.net/manual/en/datetime.add.php ?
the only tricky part is to understand how this syntax work : $date->add(new DateInterval('P7Y5M4DT4H3M2S')); P7 means add 7 years H3 means add 3 hours
Once you save or update the date in your database, send a copy along with the response and in your final response document put this :
https://jsfiddle.net/o740okn4/5/
You will need to make these calls from CDN or get the scripts from git
moment.min.js
moment-duration-format.min.js
https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.12.0/moment.min.js
and
https://cdnjs.cloudflare.com/ajax/libs/moment-duration-format/1.3.0/moment-duration-format.min.js