I've been thinking lately about what might happen in Book 7, like everyone else, and I'm working on a theory about time travel. You might scoff at my idea, I once thought Harry wouldn't/shouldn't/couldn't time travel again either, but JKR hasn't shut down that path. Matter of fact, when asked about the possibility of another time travel sequence, she said she couldn't answer.
Meanwhile, we know Harry has to learn more about what happened in the past before he can confront Voldemort. It's part of the means to an end. A pensieve only works if you can gather all the memories you'd need, and though he might be able to gather several, some memories have 
been lost (along with the people who carried them). Other memories will be protected and not shared. Still others might be tampered with, like the one Slughorn gave to Dumbledore. Harry could read up on history (recent and ancient), but what he finds in books and periodicals might be (um, yeah... will be) tainted with extreme bias. Besides, he wants to see things firsthand that have only been guessed about because the parties involved either can't or won't tell the story. What can a wizard do to learn about past events at his own leisure and without the veil of someone else's preconceptions? I mean, it's hard enough to deal with one's own prejudices...and all of the clocks are ticking. He can travel back into the past.
In PoA, Hermione uses a time-turner to "make time" for all of her coursework. Later Harry and Hermione travel back about 3 hours, their actions saving lives (and souls). Might Harry, in Book 7, travel back much farther in time?
Basically, I'm trying to see if canon will support the idea of Harry going back all the way to October 31, 1981...to see for himself what happened the night his parents were killed.
This is a tall order, I know. Many questions must be answered, like:
1] Does he "travel" alone or does he take trusted friends with him, and does he travel light or take as many handy items as he can carry on his person?
2] Can he confide in anyone from the past that he's from the future?
3] Will he take on a fake identity and interact with people, or will he have to stay physically hidden and isolate himself completely?
4] Where will he live and how will he provide for himself?
5] How long must he stay in the past? In other words, once he's in the past and has accomplished what he intended can he speed up time to return to the present, having barely aged, or does he have to spend roughly 16 years in temporal isolation from those left behind, making him much older than his peers when he comes back?
6] What will time travel back that far gain him? Sirius once said some things are worth dying for, so what's worth reliving for?
7] How will his actions affect the outcome while he's "living in the past"? What bits of canon can give us clues that he is there, not changing things (since PoA showed us that can't happen) but making things happen as they do? 
8] What vehicle will he use to travel through time...a time-turner that hasn't been destroyed...or something else entirely?
9] From a writer's perspective, how can JKR manage cramming so much time and experience (if she intends for Harry to spend an extended amount of time in the past) into 800 pages or less...when OotP, covering a single year, was longer than that?
10] How can the septology cover 7 consecutive years if the 7th book ends up covering several years?
I'm sure there are other questions, and I'll continue to look for them, as well as answers to all the questions. I'll post my "findings" in several segments.
Here, I wish to revisit part of the numerology reading I have been working on for Harry, specifically what I found and said about Soul Urge and Inner Dreams. This will address question #6 (and to a lesser extent #7) from above. Harry's number for both personality aspects is 7, which suggests isolation to gain knowledge and wisdom. At the time of my original numerology post, I thought the reading must be whack because surely Harry just wants a family. However, we must remember that the Mirror of Erised only shows us our deepest desire for the moment. Harry saw his parents and other relatives because he had no 
family to speak of, and it created a hole that needed to be filled. Since then he has basically been adopted by the Weasley family and might end up marrying Ginny. If you look at Harry standing around all the Weasleys, what do you see? A young wizard who looks a lot like his dad, a young (and very popular) witch who has red hair (like his mom), and several of the witch's relatives, also possibly having red hair -- you see a grouping that looks suspiciously similar to what Harry originally saw in the Mirror of Erised! Looks like he has essentially fulfilled that desire already.... What does Harry see at the end of PS/SS? Himself with the Philosopher's Stone, and he fulfills that desire immediately.
So, what am I getting at? If Harry looked into that mirror again, say early on in Book 7, what would he see? Himself standing over a dead Voldemort (and possibly a dead Snape, but I'd rather not think about that too much)? Maybe, but isn't that the final goal? What if there was something more presssing, like a desire to be prepared for the confrontation? He might see himself surrounded by supporters and arsenal (magical and otherwise). Or maybe we should consider what he says about Godric's Hollow. He wishes to return there because it's where his journey begins... spiritually, if you will. He might see himself amongst the ruins of the house 
where the attack took place or at their "gravesite", taking in the sight, recovering memories long-forgotten, mourning his parents, and gaining some sense of closure. What if he visualizes his desire to destroy the remaining horcruxes? He might see himself with artifacts, such as the locket and the cup, and Nagini. (On a side note, could the mirror tell him what the fourth horcrux is? Not a road I wish to walk, since canon is skimpy on that mirror....)
Preparation for battle...spiritual and emotional healing...horcrux hunt.... What will each of these "tasks" require? Time, and probably plenty of it. To some extent, isolation. Some gain in 
knowledge and wisdom, too. With this in mind, perhaps the Soul Urge and Inner Dreams results weren't as unreasonable as I first thought. Another part of the numerology reading was Birthday. It said he likes to travel and doesn't like to be alone. This sure lets him travel (space and time), though he might have to deal with extreme loneliness. Well, you can't have everything, can you now? (Sorry, I just had to use a pic of the tardis here. It's too cool...I told you I was a nerd.)
So, with four horcruxes to find and destroy, a final confrontation to prepare for, and his parents' "graves" to visit, wouldn't Harry's greatest immediate desire be for the time and opportunity to do all of these things? If Book 7 followed the same timespan as previous books in the series, how could Harry possibly accomplish his goals? Harry has never had to do so much, not on such a grand scale anyway, in one book. This means Book 7 would need to cover not a year in Harry's life but years, plural.
Here's where we get possible answers to #9 and #10 above. How lengthy must the book be to do this? JKR is trying her darndest to keep the length of Book 7 to no more than that of OotP, and she's already had to break two chapters into four. How can she fit so much time into so "few" pages? Give up the day-to-day pace of the previous books, where days or weeks might get skipped, and trade it for skipping months at a time, highlighting individual accomplishments and progress, as well as adversities and setbacks.
How can JKR have Harry spend extra years readying himself for the final showdown while the septology maintains an overall timespan of seven years? She sends him far enough back in time to prepare, while the characters remaining in the present are caught in temporal 
stasis. When he returns he battles Voldemort and the book ends in summer, roughly a year after it began. Besides, the timeline for the septology was never really 7 years to begin with. In case you forgot, PS/SS started October 31, 1981 and ended the summer of 1992. The first two chapters are not treated as a look into the past, but the present. Chapter three skips ahead into 1991. So, PS/SS actually covers a little over 10 years. We do learn about some things that happened to Harry during those 9 skipped years -- some accomplishments, some adversities -- all presented to us throughout the books as memories.
Here's a bit more regarding question #7 (though I'll address this issue in great detail as a separate post). Though we'd still see the world through Harry's eyes in Book 7, his perspective will have changed. He will see past events in his life from the outside and get to witness other events his younger self wasn't a party to. It's like he fell into a Pensieve filled with one really long memory.... Perhaps Harry's Pensieve lessons with Dumbledore serve a larger purpose than we might have previously thought. From peering into the Pensieve Harry knows what it's like to see into the past but not be able to interfere or to 
be noticed. From his time travelling with Hermione he has also found that when "cause=interfering", "effect=what ended up happening anyway". Let's not forget that the trio was alarmed by pebbles hitting Hagrid's window, and that those pebbles were actually thrown by an older Hermione. Buckbeak never died, the trio just thought he had; Harry and Hermione's actions had already saved him. Harry knew to cast his Patronus because he'd already seen it.
To be continued in a later post....
I want to start this post out with an excerpt from MuggleNet/Leaky Cauldron's interview with JKR:
Requirement, or "come and go room", in order to travel back in time directly, or that he could use the RoR to supply him with anything he'd need for the trip? In OofP, Harry's DA practice room seems to have taken or copied Moody's Foe Glass. Why couldn't the room supply Harry with a working time-turner or some other time travel device?
