PHP subtract unknown time from datetime - php

Question

So, I'm creating a booking system. When I retrieve this booking from the database, I need to check if the current date and time is closer to the actual booked date and time.
On the admin dashboard, the admins specify how much time earlier the client can make a checkin, let's say for example, 30minutes. But this time can be different. Can be 1hour, 2hours, 10minutes.
When I get the result from the database I get them like this:
$date_schedule = '2021-03-25 15:40:00'; // Can be any date in the future as well;
$time_to_check = '00:30:00'; // Can be '01:05:00', whatever the admins set as time_to_check;
// Expected result
'2021-03-25 15:10:00';
I tried subtracting this but I didn't made it work.. This is what I did.
$current_date = date("Y-m-d H:i:s");
$booking_date = '2021-03-25 15:00:00'; // From database
$time_to_check = '00:30:00'; // From database
$hours = explode(':', $time_to_check);
$data_check = date($booking_date, strtotime('-' . $hours[0] . ' hour -' . $hours[1] . ' minutes'));
But with this, $data_check returns the same value as $booking_date, it's not subtracting the time.

Answer 1

Convert your date to DateTime to make some operations on it :
function changeDate($date, $interval) {
$datetime = new DateTime($date);
$values = explode(':', $interval);
$datetime->modify("-$values[0] hours -$values[1] minutes -$values[2] seconds");
return $datetime->format('Y-m-d H:i:s');
}
$date = changeDate('2021-03-25 15:00:00', '00:30:00');
echo $date; // 2021-03-25 14:30:00
$date = changeDate('2021-03-25 15:00:00', '01:30:00');
echo $date; // 2021-03-25 13:30:00
$date = changeDate('2021-03-25 15:00:00', '02:30:15');
echo $date; // 2021-03-25 12:29:45
You can find documentation here https://www.php.net/manual/en/book.datetime.php

Answer 2

Just convert the timestamp to Unix time, and then subtract 30 minutes in seconds (30 * 60) from the Unix time.
Like this:
$date = '2021-03-25 15:10:00';
$timestamp = strtotime($date);
$timestamp = ($timestamp - (30 * 60));
echo gmdate("Y-m-d H:i:s", $timestamp);
EDIT: If you are in an odd timezone, like me (GMT+0100) add or subtract difference;
$timestamp = (($timestamp - (30 * 60)) + (1 * 60 * 60))