This code set the preparation days to 2 days when it is saturday and user selected the delivery type "Delivery"

change-preparation-days.php

add_filter('pisol_dtt_setting_filter_pi_order_preparation_days', function($preparation_days){

	$type = pi_dtt_delivery_type::getType();
	$today = current_time('Y/m/d');
	$todays_day = date('w', strtotime($today));

	if(($todays_day == 6 || $todays_day == 5) && $type == 'pickup'){
		if(class_exists('pisol_pldt_location')){
			$location = pisol_pldt_location::getSavedPickupLocation();
			if($location != 5073){
				$preparation_days = 2;
			}
		}
	}

	return $preparation_days;

},200,1);