The default time required between multiple comments from the same user/IP is 15 seconds. If the user posts the second comment faster than 15 seconds after the first comment, the comment flood message is triggered.
Below is an example showing how to change the default time.
Source: https://wordpress.org/support/article/faq-working-with-wordpress/#how-do-i-prevent-comment-flooding

function wpdocs_dam_the_flood( $dam_it, $time_last, $time_new ) {
    if ( ( $time_new - $time_last ) < 300 ) { // time interval is 300 seconds
        return true;
    }

    return false;
}
add_filter( 'comment_flood_filter', 'wpdocs_dam_the_flood', 10, 3 );