start expiration period not on registration, but when assigned to role

Ok I got it now, some custom code in the functions.php

Please keep on developing this plugin, I would love to have different expire options, like different times for registration and my case on purchase of a product.

Yes here it is. It is already adapted for pieregister. But if you use a diffrent add_action you can start the function otherwise

// Function to add expiry on registration to a user role  $current_user->ID
function new_registerd_member( $user ) {
	//$current_user = wp_get_current_user();

	//$user = new WP_User( $current_user->ID );

	// Remove role
	//$user->remove_role( 'subscriber' ); 

	// Add role
	//$user->add_role( 'mycustomrole' );

	// This adds the expire user stuff to the role  posible date_in_block 'years' 'months' 'weeks' 'days'
	global $expire_users;

	$expire_settings = $expire_users->admin->settings->get_default_expire_settings();

	$expire_data = array(
				'expire_user_date_type'         => $expire_settings['expire_user_date_type'],
				'expire_user_date_in_num'       => 1,
				'expire_user_date_in_block'     => 'months',
				'expire_user_date_on_timestamp' => $expire_settings['expire_timestamp'],
				'expire_user_role'              => $expire_settings['expire_user_role'],
				'expire_user_reset_password'    => $expire_settings['expire_user_reset_password'],
				'expire_user_email'             => $expire_settings['expire_user_email'],
				'expire_user_email_admin'       => $expire_settings['expire_user_email_admin'],
				'expire_user_remove_expiry'     => $expire_settings['expire_user_remove_expiry']
	);

	$user = new Expire_User( $user->ID );
	$user->set_expire_data( $expire_data );
	$user->save_user();
}

add_action( 'pie_register_after_register_validate', 'new_registerd_member', 10,1 );

Hope this helps