I suppose it could be any length of time at all, to us. And yet, from the photon’s POV, it would seem instantaneous–
that it delivered–
Enlightenment!
Whether you want to explain the “known unknowns” through non-material or material means still leaves you with the problems you stated yourself:
Replace “non-material” / “non-physical” in the above with “unknown stuff”, and I don’t know that you’ve really gotten anywhere. The fact that there are two things we don’t understand (namely, consciousness and dark matter/energy) doesn’t mean they have anything to do with one another, especially when no mechanism is put forth. Also, we do know some things about consciousness and about dark matter and about dark energy, and none of the things we know suggest a connection. Also, there are way more known unknowns in nature, and why these seemingly unrelated ones should be singled out as being connected seems artificial, given no evidence or supposed mechanism.
I don’t know of any historical cases of this.
Well of course you don’t–they’ve all been classified. 
I have heard of cases of public research being classified, typically applied mathematics dealing with encryption algorithms. I don’t know what the legal basis is if the researchers involved have not signed contracts to maintain a security clearance. I’d think there’s First Amendment issues involved.
I just discovered this thread!
What is the current thinking on preons, which have been postulated as being more fundamental than quarks? For that matter, what about layers beneath leptons and gauge bosons?
These questions may be from a position of ignorance, but what’s going on with the vacuum energy and virtual particles popping into and out of existence? On average, how long do particles and antiparticles exist before annihilating each other? What is the density at which they appear (i.e. number of “ex nihilo” events per unit area per unit time?) Is this a constant regardless of where in time or space we look? During the (brief) time they exist, do they exert any gravitational effect on their surroundings? Does one member of a pair ever annihilate an already existing antiparticle of its same kind, leaving its twin to persist? Are there any theoretical ways of separating pairs before they annihilate each other?
prof. Stephen Hawking proposed a method of Black Hole radiation…aptly named Hawking Radiation…in which a quantum singularity sheds mass at the Event Horizon: a virtual particle pair spontaneously erupts into existence near the horizon, one of the pair falls in and the other escapes, essentialy taking one particle’s worth of mass from the singularity.
Indeed, I mean not infer nor imply anything beyond an incremental change toward the positive with regard to legitimizing the idea of dualism. At most, it’d be partially resuscitating an all-but-dead philosophy back into the mind philosophy game—not in the lead, or perhaps even a prime contender, but at least in possession of a heartbeat.
Let me just speak in generalities, mainly because I’m not qualified to talk specifics. I accept your stance that we can’t assume a relationship between two things we don’t understand (e.g. consciousness and dark matter), particularly when no mechanism is put forth. But, at least it gives the possibility, minute though it may be, of a scientifically sound relationship between two things that are believed to exist, but whose makeup is, so far, unknown. Compare that to trying to forge a relationship, as substance dualism proponents have done historically, between something we know to exist (i.e. brain matter) and the notion of something I believe most scientists would scoff at, a non-material consciousness. The difference: a non-material consciousness could not exist; an exotic material consciousness of unknown design could exist—it may not, but at least it could. Why it *should *needs further exploration.
Why do I think there may be a small, but significant difference between these two pathways? Primarily because I believe the jury is still out on a definitive materialistic MOA relationship between mind and brain. Neurophysiologists and anatomists know a great deal about the gross structure and workings of the brain and, I’m sure, particle physicists know a great deal about the makeup of the brain at the sub-atomic level, and there are plenty of specialists to study the brain between the gross and subatomic extremes. But still, the structure and process of consciousness and its relationship to the brain is still very much unknown. Most physicalists may hold that the mind-brain relationship does exist at the purely known physical level and it’s just a matter of time until we understand it completely. That may be true, but then again, the relationship may be at a deeper level with material we don’t understand or perceive yet.
So we start with two potential pathways: Dualism: material brain & non-material mind vs. Physicalism: material brain is all there is, consciousness is just a higher level/lower lever supervenience relationship. Dualism fails because non-material stuff is scientifically untenable. Pure Physicalism is somewhat weakened, IMHO, in that the MOA of consciousness and its relationship to brain matter is still not understood and certainly up for debate in the scientific community. On top of that…admittedly unscientific…and I’m certain I’m not alone in thinking this, but, it just feels that consciousness is more than simply a process overlying brain matter as we know it—doesn’t it? It’s a gut reaction I think we all share to some degree, at particular contemplative moments in our lives. 
Enter the 96% of the yet unknown mass-energy of our universe. I can’t tie my consciousness to something that doesn’t exist (i.e. non-material stuff); I have trepidation tying it to something as seemingly mundane as the known particles that make up a human brain (not unlike arguing that a pile of cinder blocks could compose Beethoven’s 9th); but give me some esoteric mass-energy stuff of unknown, possibly bizarre quality…I can wrap my mind around that, literally. IMO, this route doesn’t necessarily win on its own merit, but by default. We can even do away with the unscientific sounding moniker, dualism—with all stuff being of a material nature, some just more exotic than the rest, we can just think of it as being an expanded type of physicalism.
And, lest anyone accuse me of being a frustrated theist looking for a place to hide god, I’m not. In fact, if (a huge if) consciousness can, or does survive beyond physical death (the regular matter part of our body), I see no reason to involve an omniscient middleman in the process. Consciousness may evolve and survive through time in much the same manner as DNA does via biological evolution…only, you know, without the sex—unless thinking about sex is what it’s all about. 
I’m getting “serious” again. (With this question it may be hard to tell.)
I’m basing this on a speculation by Asimov several years back. (To simplify a scenario he presented in “I’m Looking Over a Four Leaf Clover”) Is it possible that we don’t observe a portion of space where antimatter prevails because…
There is an “antimatter cosmon” which developed *backward in time *from the Big Bang? This is based on the observation that antiparticles cn be viewed as travelling backward through time… so why not a whole “universe” in which they dominated?
Please don’t laugh very hard. 
What is your take on Horava’s theory of gravity; that as one looks at spacetime at the microscopic quantum level, space and time “decouple”…is that right?
http://dapht.blogspot.com/
According to this, the new theory seems to offer an explanation to the Dark Matter/Dark Energy mystery.
Just checking in. It’s been an unusually busy week, but I’ll catch up with the thread in a few days…
Another question in the meantime.
We’ve been informed that String Theory (if it even qualifies as “theory”) would need to be tested at several powers of ten smaller than we have so far tested anything. I think it’s a matter of so many powers of ten smaller than a nucleon’s diameter. (I’m assuming that a nucleon, such as a neutron, has a diameter in that we can specify the typical radius of quark confinement.)
It makes sense that it is really only a hypothesis, and even that it must remain so. But can we be sure?
At one time it was considered impossible to explore an atom. Does it seem at all likely to you that someday the needed probing apparatus will exist?