[php] How can I check if the current date/time is past a set date/time?

I'm trying to write a script that will check if the current date/time is past the 05/15/2010 at 4PM

How can I use PHP's date() function to perform this check?

date_default_timezone_set('Asia/Kolkata');

$curDateTime = date("Y-m-d H:i:s");
$myDate = date("Y-m-d H:i:s", strtotime("2018-06-26 16:15:33"));
if($myDate < $curDateTime){
    echo "active";exit;
}else{
    echo "inactive";exit;
}

Since PHP >= 5.2.2 you can use the DateTime class as such:

if (new DateTime() > new DateTime("2010-05-15 16:00:00")) {
    # current time is greater than 2010-05-15 16:00:00
    # in other words, 2010-05-15 16:00:00 has passed
}

The string passed to the DateTime constructor is parsed according to these rules.

Note that it is also possible to use time and strtotime functions. See original answer.

There's also the DateTime class which implements a function for comparison operators.

// $now = new DateTime();
$dtA = new DateTime('05/14/2010 3:00PM');
$dtB = new DateTime('05/14/2010 4:00PM');

if ( $dtA > $dtB ) {
  echo 'dtA > dtB';
}
else {
  echo 'dtA <= dtB';
}

Check PHP's strtotime-function to convert your set date/time to a timestamp: http://php.net/manual/en/function.strtotime.php

If strtotime can't handle your date/time format correctly ("4:00PM" will probably work but not "at 4PM"), you'll need to use string-functions, e.g. substr to parse/correct your format and retrieve your timestamp through another function, e.g. mktime.

Then compare the resulting timestamp with the current date/time (if ($calulated_timestamp > time()) { /* date in the future */ }) to see whether the set date/time is in the past or the future.

I suggest to read the PHP-doc on date/time-functions and get back here with some of your source-code once you get stuck.