Should be in advwp_event_manager/public/templates/

taxonomy.php

<?php
/**
 * Used to display event taxonomy pages.
 */

get_header(); ?>

	<section id="primary" class="content-area">
		<main id="main" class="site-main" role="main">

		<?php 

		function advwp_edit_event_order( $orderby ) {
		  return 'mt1.meta_value, mt2.meta_value DESC';
		}
    
    // This may be the ugliest line of code ever. It is an unnecessarily complex ternary operator,
    // just a different style of writing if {} else {} statements. 
		$taxonomy 	= ( is_tax() ? ( is_tax('series') ? 'series' : ( is_tax( 'event_type' ) ? 'event_type' : ( is_tax( 'location' ) ? 'location' : ( is_tax( 'patron_type' ) ? 'patron_type' : null ) ) )  ) : null );
		$qobj = get_queried_object();

		$args = array(
		  
		  // fetch only "events""
		  'post_type' => 'event',
		  
		  // we can't orderby a meta_value if the
		  // key isn't present ... - even if we 
		  // aren't actually using 'orderby' directly
		  // in the query.
		  'meta_key' => 'advwp_start_date',
		  
		  // We define multiple keys using 'meta_query'
		  'meta_query' => array(
		    
		    // the first key, or mt1
		    array(
		      'key' => 'advwp_start_date'
		    ),
		    
		    // the second key, or mt2
		    array(
		      'key' => 'advwp_start_time'
		    )
		  ),
		  'nopaging' => true,
		  $taxonomy => $qobj->slug
		);

		add_filter( 'posts_orderby', 'advwp_edit_event_order' );
		$the_query = new WP_Query( $args );
		remove_filter( 'posts_orderby', 'advwp_edit_event_order' );


			if ( $the_query->have_posts() ) : ?>

			<header class="page-header">
				<?php
					the_archive_title( '<h1 class="page-title">', '</h1>' );
					the_archive_description( '<div class="taxonomy-description">', '</div>' );
				?>
			</header><!-- .page-header -->

			<?php
			// Start the Loop.
			while ( $the_query->have_posts() ) : $the_query->the_post(); 

    // Once within the loop, we can create fetch information from the post's custom fields
    // Some of this is contingent on whether our event is All Day or Multi-Day,
    // so we first need to declare variables for these values. In PHP, if you
    // want to pass a value between conditions (if / then statements), they need
    // to be declared outside of those conditions first. So even though we 
    // don't know yet if an event is All Day or Multi-Day, we just have to
    // establish a starting point. Let's assume that the default is that
    // events are neither All Day or Multi-Day.
    $allday = false;
    $multiday = false;
    
    // The reality as to whether these variables are true or not is
    // stored is stored in the checkboxes, which I happened to call
    // 'scheduling options'. So let's get that first:
    $scheduling_options = get_post_meta( get_the_ID(), 'scheduling_options', true);
    
    // All events have a start day, so let's get that
    $start_date = get_post_meta( get_the_ID(), 'advwp_start_date', true );
    
    // The full picture of what is the beginning and end of an event
    // isn't just the day - it's the time. To be able to sort and organize events
    // by start time, especially when they are in the same day, we need to
    // have a value that is both the day of the event and the time of the event.
    // We don't know that just yet, but let's create those variables and set
    // their default value as just the day of the event - which we already have in
    // $start_date.
    $start = $start_date;
    $end = $start_date;
    
    // Now, based on the value of our $scheduling_options, we will figure out
    // whether custom fields exist for start and end time, and set those. This
    // begins with the condition that there are NO scheduling_options, meaning
    // neither of the boxes were checked - or the default state of the event.
    
    // The !$scheduling_options means "No value for $scheduling_options".
    if ( !$scheduling_options ) {
      $start_time = get_post_meta( get_the_ID(), 'advwp_start_time', true);
      $end_time = get_post_meta( get_the_ID(), 'advwp_end_time', true );
      
      // Now with a $start_time and $end_time, we can update our
      // $start and $end variables to include day and time
      $start = $start_date . $start_time;
      $end = $start_date . $end_time;
    
      
    } else { // However, if there ARE $scheduling_options
    
      // If the "All Day" box was checked, let's update
      // $allday to true
      if ( in_array( "allday", $scheduling_options) ) :
        
        $allday = true;
        
      else : // Otherwise, update our $end variable
        
        $end = get_post_meta( get_the_ID(), 'advwp_end_date', true ) . get_post_meta( get_the_ID(), 'advwp_end_time', true);
      
      endif;
      
      // If the "Multi-day" box was checked ...
      if ( in_array( "multiday", $scheduling_options) ) :
        
        $multiday = true;
        $start = $start_date;
        $end = get_post_meta( get_the_ID(), 'advwp_end_date', true);
      
      endif;
    }

			?>

			<article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
			<?php
			// Post thumbnail.
			twentyfifteen_post_thumbnail();
			?>

			<header class="entry-header">
			  <?php
			    if ( is_single() ) :
			      the_title( '<h1 class="entry-title">', '</h1>' );
			    else :
			      the_title( sprintf( '<h2 class="entry-title"><a href="%s" rel="bookmark">', esc_url( get_permalink() ) ), '</a></h2>' );
			    endif;
			  ?>
			</header><!-- .entry-header -->

			<div class="entry-content">
			  <?php

	            // To ensure that we are successfully fetching our custom
	            // fields, we'll 'echo' - or print -- the variables we stored 
	            // above.
	            echo date( 'l, F jS', strtotime( $start ) ) . ' from ' . date( 'g:i a', strtotime( $start ) ) . ' - ' . date( 'g:i a', strtotime( $end ) ) . '<br>';


			    the_content();

			    wp_link_pages( array(
			      'before'      => '<div class="page-links"><span class="page-links-title">' . __( 'Pages:', 'twentyfifteen' ) . '</span>',
			      'after'       => '</div>',
			      'link_before' => '<span>',
			      'link_after'  => '</span>',
			      'pagelink'    => '<span class="screen-reader-text">' . __( 'Page', 'twentyfifteen' ) . ' </span>%',
			      'separator'   => '<span class="screen-reader-text">, </span>',
			    ) );
			  ?>
			</div><!-- .entry-content -->

			<?php
			  // Author bio.
			  if ( is_single() && get_the_author_meta( 'description' ) ) :
			    get_template_part( 'author-bio' );
			  endif;
			?>

			<footer class="entry-footer">
			</footer><!-- .entry-footer -->

			</article><!-- #post-## -->

			<?php
			// End the loop.
			endwhile;

			// Previous/next page navigation.
			the_posts_pagination( array(
				'prev_text'          => __( 'Previous page', 'twentyfifteen' ),
				'next_text'          => __( 'Next page', 'twentyfifteen' ),
				'before_page_number' => '<span class="meta-nav screen-reader-text">' . __( 'Page', 'twentyfifteen' ) . ' </span>',
			) );

		endif;
		?>

		</main><!-- .site-main -->
	</section><!-- .content-area -->

<?php get_footer(); ?>