if ( $the_query->have_posts() ) {
              while ( $the_query->have_posts() ) {
                $the_query->the_post();
                $meta = get_post_meta($the_query->post->ID);

                $start = date('G',strtotime($meta['start'][0]));
                $end   = date('G',strtotime($meta['end'][0]));   
             
                $arr[date('Y/m/d',strtotime(get_the_date()))] = array(
                                'start' => $start,
                                'end'   => $end
                                );
              }
        }

Array
(
    [2021/10/28] => Array
        (
            [start] => 0
            [end] => 8
        )

    [2021/10/27] => Array
        (
            [start] => 0
            [end] => 8
        )

    [2021/10/25] => Array
        (
            [start] => 0
            [end] => 8
        )

    [2021/10/22] => Array
        (
            [start] => 0
            [end] => 8
        )

    [2021/10/21] => Array
        (
            [start] => 0
            [end] => 8
        )

    [2021/10/20] => Array
        (
            [start] => 0
            [end] => 8
        )

    [2021/10/19] => Array
        (
            [start] => 0
            [end] => 8
        )

)

Solution - 1

can you share the desired output of the array when date date spans from one day to the next ?

Solution - 2

To get the desired array, firstly, we need to arrive at the difference between the start and end dates. And then, loop over the number of days between start and end dates with few conditions that fits our requirement and finally feed them into the array. Here is a code you can try:

if ( $the_query->have_posts() ) {
    while ( $the_query->have_posts() ) {
        $the_query->the_post();
        $meta = get_post_meta($the_query->post->ID);
        
        $start = date('G',strtotime($meta['start'][0]));
        $end = date('G',strtotime($meta['end'][0]));
        
        $start_datetime = strtotime($meta['start'][0]);
        $end_datetime = strtotime($meta['end'][0]);
        
        $start_date = date('Y/m/d',$start_datetime);
        $end_date = date('Y/m/d',$end_datetime);
        
            // Calculating the difference in timestamps
            $diff = $end_datetime - $start_datetime;
              
            // 1 day = 24 hours
            // 24 * 60 * 60 = 86400 seconds
            $daysbetween = (abs(round($diff / 86400)) +1);
            // echo $daysbetween;
        
        for ($i = 1; $i <= $daysbetween; $i++) {
            if (($i == 1 ) and ($i == $daysbetween)) {
                // single date
                $datekey = $start_date;
                $startval = $start;
                $endval = $end;
            } 
            if (($i == 1 ) and ($i != $daysbetween)) {
                // more days exist, this is first date
                $datekey = $start_date;
                $startval = $start;
                $endval = '23';
            } 
            if (($i > 1) and ($i < $daysbetween)) {
                // days in between
                $datekey = date('Y/m/d', strtotime($start_date .'+' .($i-1) .' days'));
                $startval = '0';
                $endval = '23';
            }
            if (($i > 1) and ($i == $daysbetween)) {
                // the last date
                $datekey = $end_date;
                $startval = '0';
                $endval = $end;
            }

            //push the item into your array
            $arr[$datekey] = array(
                'start' => $startval,
                'end'   => $endval
                );
            
        }
    
    
    }
}

Array
(
    [2014/08/12] => Array
        (
            [start] => 9
            [end] => 23
        )

    [2014/08/13] => Array
        (
            [start] => 0
            [end] => 11
        )

)