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publish_future_post is an action triggered when a post is transitioned from 'future' to 'publish' status (see Post Status Transitions)
add_action('publish_future_post', 'my_test_future_post'); function my_test_future_post($post_id) update_post_meta( $post_id, 'hook_fired', 'true' ); }
Important: As the links below explain, the action sends in the post_id of the post that transitioned from future to published so you can act on it. Your hook function must declare the parameter (e.g. $post_id).