I've seen a lot of posts where people are dieing to be able to add searching of future posts in addition to their published posts - mainly for event related items.
I can't tell you how it is technically done, but if you don't mind relying on a plugin, you have to (and I did) install a plugin called "No Future Posts": http://wordpress.org/extend/plugins/no-future-posts/
It is an older plugin (2009 - eep!), but I can confirm it works in WP 3.3.1
I'm just hoping this shows up in your search for answers!