Scripts should be enqueued on wp_enqueue_scripts action hook, which runs after init action. So dequeuing on init won’t work because sripts are not enqueued yet. Before enqueued scripts are printed, wp_print_scripts action is triggered so you can dequeue or unregister scripts safely at this moment:
add_action( 'wp_print_scripts', 'drw_timelinr_dequeue' );
function drw_timelinr_dequeue () {
wp_dequeue_script('jquery.timelinr');
}
add_action('wp_enqueue_scripts', 'drw_timeline_js');
function drw_timeline_js () {
wp_enqueue_script('jquery.timelinr2', get_template_directory_uri() . '/js/jquery.timelinr-1.0.js', array( 'jquery' ));
}