Cannot display single.php of a future (scheduled) post

Hello
I am working with a child theme of twentyeleven.
I would like to show also future post throughout my website.

I was using:

add_Action('pre_get_posts' , 'include_future_posts');

function include_future_posts($query)
{
    $query-> set('post_status', array('publish',  'future'));
}

and it works for category.php
but not for single.php.

Anyone has an idea?
Thanks :))