Setup Level 3 to start next Monday and end the following Monday with Paid Memberships Pro.

pmpro_checkout_end_date_example.php

/*
	Setup Level 3 to start next Monday and end the following Monday

	Requires PMPro 1.8.9 or higher.

	Add this code to your active theme's functions.php or a custom plugin.
*/
//startdate
function my_pmpro_checkout_start_date($enddate, $user_id, $level) {
	if($level->id == 3)
		$startdate = "'" . date('Y-m-d', strtotime('next Monday', current_time('timestamp'))) . "'";

	return $startdate;
}
add_action('pmpro_checkout_start_date', 'my_pmpro_checkout_start_date', 10, 3);

//enddate
function my_pmpro_checkout_end_date($enddate, $user_id, $level, $startdate) {
	if($level->id == 3 && $level->expiration_number > 0)
		$enddate = "'" . date("Y-m-d", strtotime("+ " . $level->expiration_number . " " . $level->expiration_period, strtotime(trim($startdate,"'")) )) . "'";

	return $enddate;
}
add_action('pmpro_checkout_end_date', 'my_pmpro_checkout_end_date', 10, 4);