在您的functions.php中

function date_compare($id){
    
    $start_date = get_field('beginning_date', $id);
    $end_date = get_field('completion_date', $id);
    
    $start_year = wp_date("Y", strtotime( $start_date ) );
    $end_year = wp_date("Y", strtotime( $start_date ) );
    
    $start_month = wp_date("n", strtotime( $start_date ) );
    $end_month = wp_date("n", strtotime( $start_date ) );
    
    $date_output = '';
    
    $start_date_format = "l, F j, Y";
    
    if( $start_date && $end_date ){
        
        if( $start_year == $end_year && $start_month == $end_month ){
            $start_date_format = "l j";
        }
        elseif( $start_year == $end_year){
            $start_date_format = "l, F j";
        }

    }
    
    
    if( $start_date ){
        $date_output .= wp_date($start_date_format, strtotime( $start_date ) );
    }
    
    if( $end_date ){
        $date_output .= ' - ' . wp_date("l, F j, Y", strtotime( $end_date ) );
    }
    
    return $date_output;
}

在主题中：

echo date_compare($post->ID);