Another possible reason to have a time-buffer in a world simulator (which, btw, I don't believe the HP:MORverse is) is that the simulation doesn't actually do everything in real time.
Rather, you may have situations where process A and process B are defined as taking the same number of simulated time-slices, but process B takes more actual time to simulate for whatever reason, and so the simulation of process A is halted until process B catches up. (This presumes that it's not possible to reallocate simulated processes across simulating resource threads with arbitrarily fine granularity.)
Which means that at any given real-world moment, some parts of the simulation are at timeslice T, some parts are at timeslice T+1, and so forth. The six-hour limit might simply reflect the typical spread, and simulated time-travel might be a hacking of the system that is bound by that spread, rather than an explicitly simulated capability with an explicitly simulated upper bound.
Something like this is true of the only reality-simulating system we know of, namely our own brains. For example, color phi is a kind of simulated time travel where, in response to a perceived event E1 at time T, your brain constructs an illusory event E2, which you experience as occurring before T. This works because different parts of your brain construct your experience of time T at different rates, and tag those parts as occurring at T; the experience of simultaneity is constructed by your brain.
Which means that at any given real-world moment, some parts of the simulation are at timeslice T, some parts are at timeslice T+1, and so forth.
If the six-hours is to avoid too much time-skew, it's a hack and one would expect better from simulation-builders.
There are plenty of ways to efficiently calculate differing time-space regions, using lazy evaluation or equivalents thereof. For example, the famous Hashlife algorithm for Conway's Game of Life does exactly that - different regions can be billions or trillions of generations apart thanks to memoizat...
- This thread has run its course. You will find newer threads in the discussion section.
Another discussion thread - the fourth - has reached the (arbitrary?) 500 comments threshold, so it's time for a new thread for Eliezer Yudkowsky's widely-praised Harry Potter fanfic.
Most of the paratext and fan-made resources are listed on Mr. LessWrong's author page. There is also AdeleneDawner's collection of most of the previously-published Author's Notes.
Older threads: one, two, three, four. By tag.
Newer threads are in the Discussion section, starting from Part 6.
Spoiler policy as suggested by Unnamed and approved by Eliezer, me, and at least three other upmodders:
It would also be quite sensible and welcome to continue the practice of declaring at the top of your post which chapters you are about to discuss, especially for newly-published ones, so that people who haven't yet seen them can stop reading in time.