1. Visit >WooCommerce>Phone Orders>Settings>Custom fields and paste following text to 1st textarea .

 Adjust time slots to match yours!!

Delivery Date|_orddd_timestamp|date
Time Slot|_orddd_time_slot|select|00:00 - 08:00|12:00 - 19:00

2. Add this PHP code to  functions.php OR  using https://wordpress.org/plugins/code-snippets/ 

add_action( 'wpo_order_created', function( $order ,$cart ){
  $date = $order->get_meta("_orddd_timestamp");
  update_post_meta( $order->get_id(), 'Delivery Date', $date );
  update_post_meta( $order->get_id(), '_orddd_timestamp', strtotime($date) );
  update_post_meta( $order->get_id(), 'Time Slot', $order->get_meta("_orddd_time_slot") );
},10,2);