The thing to note here, is that, from the informational point of view of Dumbledore, provided he doesn't have some additional side-channel information, Scenario A and Scenario B are indistinguishable.

For Dumbledore, sure. Are the scenarios really indistinguishable for the whatever-it-is that keeps histories consistent and, presumably, enforces the six-hour rule? If not, Dumbledore has an obvious means of distinguishing between the scenarios: Attempt to travel six hours into the past, in steps of one hour, precommitting to telling someone what Amelia told him. In scenario B, the third hop will fail; in A, only the sixth.

Given no other information to strictly verify, any supposed time-traveled conversation is indistinguishable from someone not having time-traveled at all and making the information up. The true rule must depend on the actual truth of information acquired, and the actual time such information came from. Otherwise, the rule is inconsistent. It also looks at whether your use of time travel actually involves conveying the information you gained; whether such information is actually transferred to the past, not merely whether it could be. Knowing that Amelia Bones has some information about 4 hours in the future will only restrict your time travel if you would transmit that information to the past - if you would act significantly differently knowing that than you would have otherwise. If you act the same either way, then you are not conveying information.

In short, the rule is that you cannot convey information more than 6 hours into the information's relative past, but that does not necessarily mean that you cannot go to a forbidden part of the past after learning it. It merely means that you cannot change your mind about doing so after learning it. Worth noting: if you plan on going to the past, and then receive some information from 6 hours in the future that changes your mind, you have conveyed information to the past. I'm not sure how that is handled, other than that the laws of the universe are structured as to never allow it to happen.

From Chapter 6:

Harry was examining the wizarding equivalent of a first-aid kit, the Emergency Healing Pack Plus. There were two self-tightening tourniquets. A Stabilisation Potion, which would slow blood loss and prevent shock. A syringe of what looked like liquid fire, which was supposed to drastically slow circulation in a treated area while maintaining oxygenation of the blood for up to three minutes, if you needed to prevent a poison from spreading through the body. White cloth that could be wrapped over a part of the body to temporarily numb pain. Plus any number of other items that Harry totally failed to comprehend, like the "Dementor Exposure Treatment", which looked and smelled like ordinary chocolate. Or the "Bafflesnaffle Counter", which looked like a small quivering egg and carried a placard showing how to jam it up someone's nostril.

From Chapter 89:

"Fuego!" / "Incendio!" Harry heard, but he wasn't looking, he was reaching for the syringe of glowing orange liquid that was the oxygenating potion, pushing it into Hermione's neck at what Harry hoped was the carotid artery, to keep her brain alive even if her lungs or heart stopped, so long as her brain stayed intact everything else could be fixed, it had to be possible for magic to fix it, it had to be possible for magic to fix it, it had to be possible for magic to fix it, and Harry pushed the plunger of the syringe all the way down, creating a faint glow beneath the pale skin of her neck. Harry then pushed down on her chest, where her heart should be, hard compressions that he hoped was moving the oxygenated blood around to where it could reach her brain, even if her heart might have stopped beating, he hadn't actually thought to check her pulse.

The oxygenation potion also slows circulation. Did Harry accidentally kill Hermione? Would the potion have unintentionally prevented blood flow to her brain by retarding flow in her carotid artery, while unhelpfully oxygenating her neck? It makes sense that a potion designed to prevent the spread of poison would prevent movement of the blood. It's also stated that it works on "a treated area." If it's primarily meant to slow the spread of poisons from bites, the spell's "treated area" might be defined as the volume of flesh a certain distance away from the injection site.

Also, giving CPR to someone when their heart is still beating is definitely not good for them.

This is a lot like evaporative cooling of group beliefs

A person who is very intelligent will conspicuously signal that ey feels no need to conspicuously signal eir intelligence, by deliberately not holding difficult-to-understand opinions.

What does it mean when people hold difficult to understand moral opinions?

Ahem. Am I reading this right?

There's a 20-year-old human with three days left to live. They have a choice: Either they spend a million dollars having fun during those three days, or invest that million dollars in research to find a cure for their unique illness and put themselves on life support in the meantime. There is only 10% chance that a cure will be found within <10 years (after which life support fails), but if it is found, they gain all of their remaining life expectancy, which is probably more than 50 years.

You're telling us that everyone should party with the million dollars for three days, and then die.

"Call me when cryonicists actually revive someone," they say; which, as Mike Li observes, is like saying "I refuse to get into this ambulance; call me when it's actually at the hospital".

There was a time when expecting mothers did the rational thing by not going to the maternity ward. http://www.ehso.com/ehshome/washing_hands.htm#History

Resources to be devoted to cryonics and a future lifespan could also be devoted to the lifespan you are fairly sure you have right now. The situation would be more like getting into an ambulance, when there have been no known successful arrivals of ambulance trips and many known failures.

It is important to be rational about charity for the same reason it is important to be rational about Arctic exploration: it requires the same awareness of opportunity costs and the same hard-headed commitment to investigating efficient use of resources

In his Mars Direct talks, Robert Zubrin cited the shoestring budget Amundsen expedition through the Northwest Passage in comparison to around 30 contemporary government funded expeditions with state of the art steam frigates and huge logistics trains. The Amundsen expedition traveled in a cheap little sealing boat and fed themselves largely through rifles and ammunition they brought with them.

http://www.youtube.com/watch?feature=player_detailpage&v=Mm34Muv6Lsg#t=102s