Can't order posts correctly, because saving as timestamp doesn't work!

[der-lukas]

Hey!

I'm running WP 4.2.2, ACF 4.4.2 and the latest version of acf-field-date-time-picker.
Your plugin doesn't work when I'm trying to save the values as timestamps. Now I chose to save the values as strings, but this makes a problem with ordering my posts in WP Query, as you can see in this image:

http://i.imgur.com/NbeeVEp.png?1

The last of the three entries ("Bananaboat") has an earlier start-time as the once before, so it should be on top of the other two posts.

My Field Settings look like this:

http://i.imgur.com/smNEFsu.png?1

.. and my WP-Query Arguments:

$args = array (
        'post_type'              => 'event',
        'post_status'            => 'publish',
        'orderby'                => 'meta_value',
        'meta_key'               => 'von',
        'order'                  => 'ASC',
        'posts_per_page'         => -1,
);

("von" is the field name of the date-time-picker-field)

But as the value is not saved as a timestamp, it seems to have issues ordering the posts correctly...

Do you have any idea how I could go about solving this problem? I'm a little under pressure with a deadline coming up... -.-

All the best,
Lukas