In the following shortcode, I have two variable, $today and $tommorrow that are being called inside a custom meta query.

function display_prognostika_home_loop($atts, $content = null) {
    // Get all the categories
    $taxonomy = 'diorganosi';
    $today = current_time("Y-m-d");
    $tomorrow = date("Y-m-d", strtotime('tomorrow'));

    $parent_terms = get_terms ( 
    array (
        'taxonomy' => $taxonomy,
        'parent' => 0,
        'fields' => 'ids',
        ) 
    );
    
    
    $terms_list = get_terms($taxonomy,
    array (
        'hide_empty' => true, // change to true if you don't want empty terms
        'orderby' => 'name',
        'order' => 'ASC',
        'exclude' => $parent_terms,
        )
    );  

    ob_start();
    
    // Loop through the $category terms
    foreach ( $terms_list as $term ):
        
    
        $prognostika_loop = new WP_Query(
            array(
                'post_type' => 'prognostika',
                'showposts' => -1,
                'order' => 'ASC',
                'orderby' => 'prog_date_time',
                'tax_query' => array(
                    array(
                        'taxonomy'  => $taxonomy,
                        'terms'     => array( $term->term_id ),
                        'field'     => 'term_id',
                    )
                ),
                'meta_query' => array(
                    array(
                        'key'       => 'prog_date_time',
                        'value'     => $today,
                        'compare'   => '=',
                        'type'      => 'DATE',
                    ),
                ),  
            )
        );
        // output category title and posts
        if($prognostika_loop->have_posts()) {
        ?>
        
        <div class="gb-button-wrapper prognostiko-diorganosi-wrapper">

            <span class="gb-button prognostiko-diorganosi"><span class="gb-button-text"><?php echo $term->name; ?></span>
                <span class="gb-icon">
                    <svg xmlns="http://www.w3.org/2000/svg" xml:space="preserve" style="enable-background:new 0 0 27.965 27.965" viewBox="0 0 27.965 27.965"><path d="M23.43 12.929c-.021-.021-.043-.034-.064-.052-.025-.029-.047-.061-.07-.09l-6.273-6.269c-.812-.813-2.099-.845-2.871-.071-.773.772-.741 2.061.071 2.872l3.054 3.056H5.967a1.981 1.981 0 1 0 0 3.962h11.254l-3.041 3.037c-.824.826-.867 2.122-.094 2.896.775.772 2.069.731 2.895-.095l6.354-6.354c.826-.824.868-2.12.095-2.892z" style="fill:#030104"></path><path d="M13.983 0C6.262 0 0 6.261 0 13.985c0 7.721 6.262 13.979 13.983 13.979 7.724 0 13.982-6.259 13.982-13.979C27.966 6.261 21.707 0 13.983 0zm0 26.535c-6.933 0-12.551-5.619-12.551-12.549 0-6.934 5.619-12.551 12.551-12.551s12.551 5.617 12.551 12.551c0 6.93-5.619 12.549-12.551 12.549z" style="fill:#030104"></path>
                    </svg>
                </span>
            </span>

        </div>
                
        <?php
        //$cat_object = $prognostika_loop->get_queried_object();
        //$cats = $cat_object->count;
        //var_dump ($cat_object);
    
        while ($prognostika_loop->have_posts()) : $prognostika_loop->the_post();
        do_action('prognostika_loop');
        endwhile;
        }
    
        // Reset query
        $customQuery = null;
        wp_reset_postdata();

    // end the loop
    endforeach;
    return ob_get_clean();
}

add_shortcode('prognostika_home_loop', 'display_prognostika_home_loop');

I would like to set up attributes so that

[prognostika_home_loop today] - Display today's posts
[prognostika_home_loop tomorrow] - Display tomorrow's posts