Code snippet to display the number of days selected by the customer for a booking in the WooCommerce Email.

function.php

add_filter( 'woocommerce_email_order_item_quantity', 'display_number_of_days_booked_as_quantity_in_order_emails',10,2 );
function display_number_of_days_booked_as_quantity_in_order_emails($quantity,$item =array()) 
    {
        if(!empty($item) && !empty($item->get_product_id())  ) 
        {
            $product_id = $item->get_product_id();
            $from_date = $item->get_meta('From',true);
            $to_date = $item->get_meta('To',true);
            if (!empty($from_date)) 
            {
                if (!empty($to_date))
                {
                    if (is_array($from_date)) 
                    {
                        $from_date = $from_date[0];
                    }
                    if (is_array($to_date)) 
                    {
                        $to_date = $to_date[0];
                    }
                    $datediff = get_number_of_slots_selected(strtotime($from_date),strtotime($to_date),$product_id);
                }
                else
                {
                    $datediff = 1;
                }
                return $datediff;
            }
            else
            {
                return '-';
            }
        }
        return $quantity;
    }
    function get_number_of_slots_selected($book_from,$book_to,$product_id){
        $divider = get_interval_in_seconds($product_id);
        $datediff = (int)$book_to - (int)$book_from;
        return round( ($datediff / $divider) + 1);
    }
    function get_interval_in_seconds($product_id){
        $interval = 0;
        $interval_period            = get_post_meta( $product_id, "_phive_book_interval_period", 1 );
        $phive_enable_buffer        = get_post_meta($product_id,"_phive_enable_buffer",1);
        $buffer_period          = get_post_meta($product_id,"_phive_buffer_period",1);
        $prod_interval          = get_post_meta( $product_id, "_phive_book_interval", 1 );
        if( ($phive_enable_buffer == 'yes') && ($interval_period == $buffer_period) &&  $interval_period == 'minute'){
            $interval = get_buffer_added_interval($product_id);
        }
        else{
            $interval = $prod_interval;
        }
        $buffer_added_interval = $interval;
        switch ( $interval_period ) {
            case 'minute':
                $interval = 60*$buffer_added_interval;
                break;
            case 'hour':
                $interval = 60*60*$buffer_added_interval;
                break;
            case 'day':
                $interval = 60*60*24;
                break;
            case 'month':
                $interval = 60*60*24*30;
                break;
        }
        return $interval;
    }
    
    function get_buffer_added_interval($product_id){
        $buffer_before_time     = get_post_meta( $product_id, "_phive_buffer_before",1);
        $buffer_after_time      = get_post_meta( $product_id, "_phive_buffer_after",1);
        $interval_type          = get_post_meta( $product_id, "_phive_book_interval_type", 1 );
        $prod_interval          = get_post_meta( $product_id, "_phive_book_interval", 1 );
        $interval_period        = get_post_meta( $product_id, "_phive_book_interval_period", 1 );
        $buffer_before_time     = empty($buffer_before_time)?'0': $buffer_before_time;
        $buffer_after_time      = empty($buffer_after_time)?'0': $buffer_after_time;
        $interval = $prod_interval;
        if((($buffer_before_time%$prod_interval) != 0) || (($buffer_after_time%$prod_interval) != 0)){
            $interval += ($buffer_before_time + $buffer_after_time);
        }
        return $interval;
    }