Multiple categories

Replace the code in the wordpress-posts-timeline.php in its plugin folder and you can use different category in your shortcode on different pages I also added attribute to change the thumbnail size.

Sample:

[wp-timeline cat=”3″ thumbsize=”200″]

function timeline_shortcode($atts){
	extract( shortcode_atts( array(
		      'cat' => '0',
		      'type' => 'post',
		      'show' => 5,
		      'date' => 'Y',
		      'length' => 10,
		      'images' => 'no',
		      'thumbsize' => '300',
     		), $atts ) );

     return display_timeline($args,$cat,$thumbsize); //assign variables here for category and thumbnail size
 }

add_shortcode('wp-timeline', 'timeline_shortcode');

//display the timeline
function display_timeline($args,$cat,$thumbsize){

	$post_args = array(
			'post_type' => get_option('timeline_post_type'),
			'numberposts' => get_option('timeline_show_posts'),
			'category' => $cat, //get_option('timeline_post_category'),
			'orderby' => 'post_date',
			'order' => get_option('timeline_order_posts'),
			'post_status' => 'publish',
			'post_link' => get_option('timeline_post_link')
		);

		$posts = get_posts( $post_args );
		$out .=  '<div id="timeline">';
		$out .=   '<ul>';
		foreach ( $posts as $post ) : setup_postdata($post);

	        $out .=  '<li><div>';
	        	if( get_option('timeline_post_link') == 'yes'){
							$out .=  get_the_time(apply_filters( 'timeline_date_form', get_option('timeline_date_form') ), $post->ID);

	        		$out .=  '<h3 class="timeline-date">';
							if( get_option('timeline_show_titles') == 'yes'){
								$out .=  " ".get_the_title($post->ID)." ";
							}
							$out .=  '</h3><br>';

	        	} else {

							$out .= get_the_time(apply_filters( 'timeline_date_form', get_option('timeline_date_form') ), $post->ID);
							$out .=  '<h3 class="timeline-date">';
							if( get_option('timeline_show_titles') == 'yes'){
								$out .=  " ".get_the_title($post->ID)." ";
							}
							$out .=  '</h3><br>';
	          }

				if ( get_option('timeline_include_images') == 'yes' ){
					if ( featured_image($thumbsize) == true && has_post_thumbnail( $post->ID ) ){
						$out .=  '<a href="' . get_permalink($post->ID) . '" title="'.$post->title.'">';
						$out .=  '<span class="timeline-image">' . get_the_post_thumbnail( $post->ID, 'timeline-thumb' ) . '</span>';
						$out .=  '</a>';
					}
				}
				$out .=  '<span class="timeline-text">'.timeline_text(get_option('timeline_text_length')).'</span>';
				$out .=  '</div></li>';

    	endforeach;

		$out .=  '</ul>';
		$out .=  '</div> <!-- #timeline -->';
		wp_reset_postdata();
		return $out;
}

//trim text function found on http://www.jooria.com/Limit-Characters-From-Your-Text-a139.html
function timeline_text($limit){
	$str = get_the_content('', true, '');
	$str = strip_tags($str);
    if(stripos($str," ") && $limit>=0){
    $ex_str = explode(" ",$str);
        if(count($ex_str)>$limit){
            for($i=0;$i<$limit;$i++){
				$str_s.=$ex_str[$i]." ";
            }
			$str_s.="";
			return $str_s;
        }else{
			return $str;
        }
    }else{
    return $str;
    }
}

//is shortcode active on page? if so, add styles to header
function has_timeline_shortcode( $posts ) {

        if ( empty($posts) )
            return $posts;

        $shortcode_found = false;

        foreach ($posts as $post) {

            if ( !( stripos($post->post_content, '[wp-timeline') === false ) ) {
                $shortcode_found = true;
                break;
            }
        }

        if ( $shortcode_found ) {
            add_timeline_styles();
        }
        return $posts;
    }

add_action('the_posts', 'has_timeline_shortcode');

//add styles to header
function add_timeline_styles(){
	add_action('wp_print_styles', 'timeline_styles');
}
function timeline_styles(){

		wp_register_style($handle = 'timeline', $src = plugins_url('css/timeline.css', __FILE__), $deps = array(), $ver = '1.0.0', $media = 'all');
		wp_enqueue_style('timeline');
}

//check featured image theme support, add
function featured_image($thumbsize){
	if ( !current_theme_supports( 'post_thumbnails' ) ) {
		if ( function_exists( 'add_theme_support' ) ) { 

			add_theme_support( 'post-thumbnails' );
			add_image_size( 'timeline-thumb', $thumbsize, 9999 ); //80 pixels wide (and unlimited height)
			return true;
		}
	}
	else{

		add_image_size( 'timeline-thumb', $thumbsize, 9999 ); //80 pixels wide (and unlimited height)
		return true;
	}

}

//do shortcode for get_the_excerpt() && get_the_content()
add_filter('get_the_content', 'do_shortcode');
add_filter('get_the_excerpt', 'do_shortcode');

//add options page
require_once('inc/timeline_options.php');