Countdown for 7 hours then show ok - php

Question

How can I countdown for 7 hours from a variable time (I will get time from my table which is inserted with timestamp), after 7 hours from variable time I will update a table.
I need something like that
$time = 2013-05-18 02:00:00 // comes from database
$target = $time + 7hours // time from database +7hours will be 2013-05-18 09:00:00
$until = $target - $time
I need something like below code
if ($until > 0 ) {
echo "you need to wait for $until hours"
} else {
echo "time is ok"; // i will update a table
}

Answer 1

Convert time into string using strtotime($time)+25200 where 7 hour =60*60*7=25200 sec and then check and also add this file to your cron job.

Answer 2

So, considering that $database_time is the stored time, in your db, and $time_now is your computers time, this message below, just echoed out:
You Must wait 4 hours right, now
It could be done much better, but still calculates the hours from now, to db and tells you how much more, you must wait :)
<?php
$date = date_create();
$database_time = '2013-05-18 22:00:00';
$time_now = date_format($date, 'Y-m-d H:i:s');
$check = $database_time[11];
$check .= $database_time[12];
$check2 = $time_now[11];
$check2 .= $time_now[12];
$time_left = $check - $check2;
So, here is how you can manage your ourputs
if($time_left > 0) {
echo "You Must wait $time_left hours right, now";
}else{
echo "Time is OK";
}