If content is available to the general public (and thus community) only through illegal activity/pirating, then I would not say it's "easily available" for everyone. While our website is generally made of tech-savvy individuals, not every user is tech-savvy enough to understand how to safely pirate content without reprisal from the MPAA and their ISP.
There are other obstacles in the way of acquiring such content, namely the moral and ethical dilemmas for many users.
Asking questions about such works that aren't intended to have yet been seen by our community of "science fiction and fantasy enthusiasts" is needlessly exclusionary. While there may be the occasional journalist or industry person on the site that could respond to such questions, the heart of the matter is not the question or the answers, but the voting.
How can the community vote if they have no reasonable way of safely verifying the information, or otherwise trust the credibility of the responding user?
I doubt it'll be a VTC, if it's obvious you've seen the work and have a question based on actual viewing. But, I suspect you may not garner as much attention as you would as waiting until the general public has seen it. So, the community may vote by not voting at all. By asking early, you'll attract a much smaller pool of people to answer, and then might be sacrificing quality for immediate (maybe) gratification (maybe).
Personally, I'd wait until the day of release (wherever it's earliest), to ask, just to get as much attention to the question as possible, or even wait until the opening weekend is over, unless you think someone else might ask the question before you.