Check if is Post or Comment

I made a function to display the time since posting an article or comment.

function custom_posted_ago() {

    global $post;
    global $comment;

    if ( get_post_type() ) :

        $object_ID = get_the_ID( $post );

        $timeDiff = human_time_diff( get_the_time( 'U', $object_ID ), current_time( 'timestamp' ) );
        $theTime = 'span' . $timeDiff . '/span';

    else :

        $object_ID = get_comment_ID( $comment );

        $timeDiff = human_time_diff( get_comment_date( 'U', $object_ID ), current_time( 'timestamp' ) );
        $theTime = 'span' . $timeDiff . '/span';

    endif;

    $timeAgo  = sprintf( __( '%s ago', 'o2' ), $theTime );

    return $timeAgo;

}

But if I place it in a comment, it sends me the data of the post.

How can I correctly formulate my condition?