How would I go about editing this code for displaying a random post from a category for 24 hours, then switching to another random post? This would be to show a Tip of the Day.

if ( ! function_exists( 'cb_breaking_news' ) ) {  
    function cb_breaking_news(){

        $cb_breaking_filter = ot_get_option('cb_breaking_news_filter', NULL);

        if ($cb_breaking_filter == NULL) { $cb_breaking_cat = implode(",", get_all_category_ids());  } else { $cb_breaking_cat = implode(",", $cb_breaking_filter); }    
        $cb_breaking_args = array( 'post_type' => 'post', 'numberposts' => '6', 'category' => $cb_breaking_cat, 'orderby' => 'rand', 'post_status' => 'publish', 'suppress_filters' => false);
        $cb_news_posts = wp_get_recent_posts( $cb_breaking_args);  
        $cb_news = NULL;
        $cb_news .= '<div class="cb-breaking-news"><span>'. __("Tip of the Day", "cubell") .' <i class="icon-long-arrow-right"></i></span><ul>';

        foreach( $cb_news_posts as $news ) {
            $cb_news .= '<li><a href="' . get_permalink($news["ID"]) . '" title="Look '.esc_attr($news["post_title"]).'" >' .   $news["post_title"].'</a> </li> ';
        }

        $cb_news .= '</ul></div>';

        return $cb_news;
    }
}

I found some code about it online although, I can't seem to get it to work with this. The webpage just goes blank.

Hi,

you could use an external script and run it daily with cron job to set up a meta key in wp_postmeta, the name can be post_of_the_day, the value a Unix timestamp. An example:

<?php

    # config
    $dbhost = 'localhost';
    $dbname = 'database_name';
    $dbuser = 'database_username';
    $dbpass = 'database_password';

    $pdo = new PDO("mysql:host={$dbhost};dbname={$dbname}", $dbuser, $dbpass);

    $pdo->beginTransaction();

    $stmt = $pdo->prepare("SELECT id FROM wp_posts as p WHERE p.id NOT IN(SELECT post_id FROM wp_postmeta AS pm WHERE p.id = pm.post_id AND pm.meta_key = ?) ORDER BY RAND() LIMIT 1");

    $stmt->execute(array('post_of_the_day'));

    if($stmt->rowCount() > 0)
    {
        $row = $stmt->fetch(PDO::FETCH_ASSOC);

        $stmt2 = $pdo->prepare("INSERT INTO wp_postmeta (post_id, meta_key, meta_value) values(?, ?, UNIX_TIMESTAMP())");

        $stmt2->execute(array($row['id'], 'post_of_the_day'));
    }

    $pdo->commit();

With the above you select a random post between those not used as post of the day. Then change the parameters of $cb_breaking_args to select only one post and order by meta_value:

$cb_breaking_args = array(
    'meta_key' => 'post_of_the_day',
    'post_type' => 'post',
    'numberposts' => '1',
    'category' => $cb_breaking_cat,
    'orderby' => 'meta_value',
    'order' => 'DESC',
    'post_status' => 'publish',
    'suppress_filters' => false
    );

$cb_news_posts = wp_get_recent_posts($cb_breaking_args);

If it works fine you will get the post selected by the external script. Then, the meta key post_of_the_day can be used to create a list of all these posts.

The best would be to use a datetime column for the meta_value, but I'm not sure it is possible to alter or add columns to WordPress and make it work without too many changes in the core code. For this reason I chose a Unix timestamp instead of a classical date, it should be ordered correctly.

Important Note: this is not tested, I don't have a Wordpress installation and I don't know if it can work correctly, but the queries are mostly pointing to indexed keys so it should be fast.

Reference:
* https://codex.wordpress.org/Database_Description#Table:_wp_posts
* https://codex.wordpress.org/Database_Description#Table:_wp_postmeta
* http://codex.wordpress.org/Class_Reference/WP_Query#Custom_Field_Parameters
* http://codex.wordpress.org/Function_Reference/get_posts

Let us know if it's ok, otherwise if you still want to use the code you were referring to, paste it here. Bye!