Is there a word that means "not yet open"?

The most direct choice that comes to my mind is unopened:

Adj. 1. unopened - not yet opened or unsealed

…which also has the advantage of being 8 characters long.

Other terms that might work include inactive, in wait, and idle.

How about pending or imminent?

Upcoming? (Plus some filler for the 30-character limit).

How about "opening"? "The act or process of opening; a beginning; commencement; first appearance." (Wordnik.) It seems that "opening" and "not yet open" are similar in meaning, and, at same time, that word is different both from "open" and from "closed" in the sense you explained.

Unreleased gives the implication of not (yet) being available, although it is slightly longer than 8 characters.