gistfile1.phtml

<?php 
list($start, $end) = explode(' to ', $items[0]['#markup']);
$time_format = 'g:i A';
$date_format = 'F jS, Y';
$start       = strtotime($start);
$start_date  = date($date_format, $start);
$start_time  =  date($time_format, $start);
if ($end) {
   $end      = strtotime($end);
   $end_date = date($date_format, $end);
   $end_time = date($time_format, $end);
}  
?>
<div class="<?php print $classes; ?>"<?php print $attributes; ?>> 
  <?php if (!$label_hidden): ?>
    <div class="field-label"<?php print $title_attributes; ?>><?php print $label ?>:&nbsp;</div>
  <?php endif; ?>
  <div class="altered field-items"<?php print $content_attributes; ?>> 

      <div class="date-time-wrapper date">
         <span class="date-time date from"><?= $start_date; ?></span> 
         <?php if ($end_date && $start_date != $end_date) { ?> <span class="separator"> - </span><span class="date-time date to"><?= $end_date; ?></span> <?php } ?>
      </div>
          
      <div class="date-time-wrapper time">
         <span class="date-time time from"><?= $start_time; ?></span>
         <?php if ($end_time && $start_date != $end_date && $start_time != $end_time) { ?><span class="separator"> - </span><span class="date-time time to"><?= $end_time; ?></span> <?php } ?>
      </div>
  </div>
</div>