PHP在x小时后更改日期

In my code I am successful to display current date but my requirement is to show next day date after 3 hours e.g. 2017-08-17 20:00:00 the next date will be 2017-08-18 but it will show next date after spending 3 hours i.e. 2017-08-18 03:00:00 until that it remain show the old date.

I am able to add 3 hours to current date/time but I don't know how to show it after 3rd hour of the next date. Here is my code

<?php
date_default_timezone_set('Asia/Kolkata');
$time_add = date("Y-m-d H:i:s", strtotime('+3 hours'));
$time_now = date("Y-m-d H:i:s");
echo $time_now;
?> 

echo date("Y-m-d H:i:s", strtotime('+3 hours'));

The problem with your code is that you were assigning this to a variable called $time_add but then doing nothing with it.

If you want to print the current date/time after it, just use it without +3 hours:

echo date("Y-m-d H:i:s");