How to Substract time from datetime - php

Question

I am using a timezone based script where there is deadline based on timezones. Say for example a deadline is on 7th July at 6PM for a person in IST timezone. The deadline should be 1:30 less than 6pm in Dubai as per their timezone.
I have already calculated the difference between the two timezone difference. I am stuck at deducting that calculated time from the deadline time.
I have saved the timezones in +5:40 +4:00 -4:00 this format instead of using php default ones.

Answer 1

Here's what I use to add and subtract time from a date.
First of all, I get the date from the database and then convert it to a DateTime object.
$date = new DateTime($date);
I use add and a DateInterval to add time. Here's an example to add hours.
$date->add(new DateInterval("PT{$hoursToAdd}H"));
And here's and example to subtract hours intead:
$date->sub(new DateInterval("PT{$hoursToSubstract}H"));
Check this out to know how to work with DateInterval and add/subtract different times: http://php.net/manual/en/class.dateinterval.php

Answer 2

Can you explain a little more specifically what you want to do?
You want to subtract when data already on some var inside your script or you want the SQL query needed ?
If so maybe you can use this answer ---> How to subtract 3 hours from a datetime in MySQL?
The last answer of this post maybe is the one that fit the most what you need :
Assuming you have some timezone issue and know source and destination timezone, you could convert it like so
SELECT
DATE_FORMAT(CONVERT_TZ(x.date_entered, 'UTC', 'Europe/Berlin'), '%Y-%m-%d') AS date
FROM
x
ORDER BY
date ASC;