add-date-to-rss-feed.php

<?php

// Add Tribe Event Namespace
add_filter( 'rss2_ns', 'events_rss2_namespace' );
function events_rss2_namespace() {
    echo 'xmlns:ev="http://purl.org/rss/2.0/modules/event/"';
}

// Add Event Date to RSS Feeds
add_action('rss_item','tribe_rss_feed_add_eventdate');
add_action('rss2_item','tribe_rss_feed_add_eventdate');
add_action('commentsrss2_item','tribe_rss_feed_add_eventdate');
function tribe_rss_feed_add_eventdate() { ?>

  <ev:tribe_event_meta xmlns:ev="Event">
  <?php if (tribe_get_start_date() !== tribe_get_end_date() ) { ?>

    <ev:startdate><?php echo tribe_get_start_date(); ?></ev:startdate>
    <ev:enddate><?php echo tribe_get_end_date(); ?></ev:enddate>

  <?php } else { ?>

    <ev:startdate><?php echo tribe_get_start_date(); ?></ev:startdate>

  <?php } ?>
  </ev:tribe_event_meta>

<?php } ?>