We use Unix-style timestamps (i.e. the number of seconds since the Unix epoch), which is what you'll get with PKP's time() and strtotime() functions. They can be manipulated with relative ease and formatted using the PHP strftime function and Smarty date_format modifier. Math on these numbers is as simple as:
$currentTime = time();
$secondsPerDay = 60 * 60 * 24;
$currentTimePlusThirtyDays = $currentTime + ($secondsPerDay * 30);
The strftime function (see http://ca3.php.net/manual/en/function.strftime.php
) will get you the day of the week etc.
Public Knowledge Project Team