PHP Add n Minutes to Time/Date string and RETAIN timezone

After an hour exploring Stack Overflow, I’m more confused than ever (and based on the number of posts, I’m probably missing something painfully obvious). All I want to do is add n minutes to an existing date/time string (formatted as $start = ‘2022-09-10T09:00:00-07:00’) WITHOUT losing the time zone.

Based on my reading, it looks like I need to use ‘date’ and ‘strtotime’ but when I do I lose the time zone. For example …

$start = date('m:d:y H:i:s', strtotime($start . ' +90 minutes'));

…returns ’09:10:22 14:30:00′

When I try adding formatting like this to get the exact format I’m looking for…

$start = date(DATE_W3C, strtotime($start . ' +90 minutes'));

…it returns the correct format but changes the time zone: ‘2022-09-10T14:30:00+00:00’

All I am trying to do is to take ‘2022-09-10T09:00:00-07:00’ and add 90 minutes to make it ‘2022-09-10T10:30:00-07:00’. What am I missing?

>Solution :

Although there’s nothing wrong with the date and strtotime functions, they force you to deal with strings and ints which makes things muddy. Instead, if you can elevate that to a higher level thing, specifically the DateTime (or DateTimeImmutable) you can reason about things easier.

$date = new DateTime('2022-09-10T09:00:00-07:00');
$date->modify('+5 minutes');
echo $date->format(DateTime::RFC3339);

// Result: 2022-09-10T09:05:00-07:00

Demo here:

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