title: WooCommerce Subscriptions: change renewal dates after checkout
body: <p>I have 1 subscription with 3 variations.
  I'm trying to force the first renewal date depending on the variation ID that was purchased.</p>
  <p>Variation 1 (876) set to renew every day - I want first re-bill date to be 11/15/2020 12:00AM
  Variation 2 (877) set to renew every 2 days - I want first re-bill date to be 2/15/2021 12:00AM
  Variation 3 (878) set to renew every 3 days - I want first re-bill date to be 8/15/2021 12:00AM</p>
  <p>I thought the below code worked. After the order is created the next bill date DOES show one of the above dates, but it must not be registering with WooCommerce or something, because the renewals are triggering regardless of the above dates.</p>
  <p>For my test, I create an order for Variation 1, the next payment date is showing 11/15/2020, but it's renewing the next day.</p>
  <p>Hoping to get some insight from someone smarter than me. Again, the sub's next bill date is showing the above dates, but renewals are still happening early/before the above dates.</p>
  <pre><code>
  function nextpaymentdatechange( $order_id ){
      $order = wc_get_order( $order_id );
  $items = $order-&gt;get_items(); 
  foreach ( $items as $item_id =&gt; $item ) {
     $product_id = $item-&gt;get_variation_id() ? $item-&gt;get_variation_id() : $item-&gt;get_product_id();
     if ( $product_id === 876 ) {
          $subid = $order_id + 1;
          $nextdate = get_post_meta( $subid, '_schedule_next_payment', true );
          $new_date = date( 'Y-m-d H:i:s', strtotime( '2020-11-15 07:00:00', strtotime( $nextdate )) );
          update_post_meta( $subid , '_schedule_next_payment', $new_date);
     }
      else{ if ( $product_id === 877 ) {
          $subid = $order_id + 1;
          $nextdate = get_post_meta( $subid, '_schedule_next_payment', true );
          $new_date = date( 'Y-m-d H:i:s', strtotime( '2021-02-15 07:00:00', strtotime( $nextdate )) );
          update_post_meta( $subid , '_schedule_next_payment', $new_date);
      }
           else{
                if ( $product_id === 878 ) {
          $subid = $order_id + 1;
          $nextdate = get_post_meta( $subid, '_schedule_next_payment', true );
          $new_date = date( 'Y-m-d H:i:s', strtotime( '2021-08-03 07:00:00', strtotime( $nextdate )) );
          update_post_meta( $subid , '_schedule_next_payment', $new_date);
      }
           }
          
      }
     }
  } ```
  </code></pre>