After I have validated the receipt against the App Store from my PHP server, the App Store sends me back a JSON response with

"status" : 0 
"receipt" : ( .... )

One of the receipt items is "purchase_date" which contains the following string (example) "2010-02-09 19:17:04 Etc/GMT"

I'm trying to establish a subscription service and would like to add 3 months to this date and then write that expiry date into a MySQL table.

Is there a string-to-date type function in PHP that can allow me to achieve the adding of 3 months?

I have found this example which looks like it adds 1 month to a date:

$date = date("Y-m-d");// current date
$date = strtotime(date("Y-m-d", strtotime($date)) . " +1 month");

But I'm not sure how I can turn the string passed by the App Store into a PHP recognised date.