ACF Date Time Picker field: sorting and filtering posts based on the data

upcoming-events-list.php

<?php
/**
* Events custom post type has an ACF "end_date_time" which is a Date Time Picker field.
* This code creates list of all events that have not yet ended, sorted with
* the events that are ending soonest at the top of the list.
*/

$now_date_time = new DateTime( 'now', new DateTimeZone( 'Australia/Melbourne' ) );

$upcoming_events = [];

$events_query_args = array(
    'post_type' => 'event',
    'posts_per_page'=> -1
);

$events_query = new WP_Query( $events_query_args );

$event_posts = $events_query->posts;

// Save all events that haven't ended into an array
foreach ( $event_posts as $event_post ) {

    // Get event end date and time from ACF and create DateTime object
    /**
    * NOTE 
    * The default return format for the ACF Date Time Picker 
    * field ("d/m/Y g:i a") is not compatible with PHP's DateTime class.
    * Use the return format "Y-m-d H:i:s"
    */
    $end_date_time_str = get_field( 'end_date_time',  $event_post->ID );
    $end_date_time_obj = new DateTime( $end_date_time_str );

    // If event has not ended yet
    if ( $now_date_time <= $end_date_time_obj ) {

        // Add end date and time ACF data to post object
        $event_post->end_date_time_str = $end_date_time_str;

        // Save post object to array of upcoming events
        $upcoming_events[] = $event_post;
    }
    
}

// Sort events so that the events ending soonest are first in the array
usort( $upcoming_events, function( $a, $b ) {

    $a_date_time = new DateTime( $a->end_date_time_str );
    $b_date_time = new DateTime( $b->end_date_time_str );

    if ( $a_date_time == $b_date_time ) {
        return 0;
    }

    return $a_date_time < $b_date_time ? -1 : 1;
});
?>

<ul class="upcoming-events">
    <?php foreach( $upcoming_events as $event ) : ?>
        <li>
            <a href="<?php echo get_the_permalink( $event->ID ); ?>"><?php echo get_the_title( $event->ID ); ?></a>
        </li>
    <?php endforeach; ?>
</ul>