Automatically exclude categories from metabox based on title

You have chosen to tackle a hard problem for one so new to PHP. 🙂 This might get you closer to your goal:

global $wpdb;
if ( in_array( $pagenow, array('post.php', 'post-new.php') ) ) {
    foreach (get_categories() as $category) {
        $cat_time = strtotime($category->cat_name);
        if ( $cat_time < strtotime('-3 days') || $cat_time > strtotime('+2 months') )
            $exclude .= $wpdb->prepare( '%s,', $category->slug );
    }
    $exclude = substr( $exclude, 0, -1 );
    $exclusions = " ($exclusions) AND t.slug NOT IN ($exclude)" ;
}