...don't take this the wrong way, but even Harry knows better than that.
There is NO DOWN SIDE!
It may be best to hand over the time turner but you do so after having a chance to think it through. Time turner. Plan. Decide that it is better to hand over the device for now. Write your analysis down. Give it to yourself at the appropriate time. (And give it to yourself again to make the loop stable.)
If you genuinely think this is a smart thing to do in real life, it makes me seriously worry about your safety and the safety of people around you.
I have offended you by questioning the rationality of your fictional persona. My own safety is not in any danger. Every other exceptional use that Harry put the device to is risky and I would not do any of them. But giving himself a chance to think through his options in a way that would not be detected by anyone else is the trivially correct strategic option.
My own safety is secure in the short term, and medium term (human life span) but for the long term the threats to my life are human mortality and existential risk. And that's kind of what I've been counting on you to take care of (with any contribution that I could hope to make purely financial). That being the case, this conversation is quite literally scaring me. I'm not quite there yet, but the key quote from Snape is at least springing to my mind: "And I no longer trust your cunning."
Examples of stupid things to do with a Time Turner:
Now, all the above mistakes are credible for Harry to make. At least, they fit the needs of the story. But using the turner to give yourself time to think at a critical moment... not on the list. And make no mistake, giving up one of the most powerful super-powers (even in the weakened 6h form) is an extremely critical moment.
But now another lesson from Harry Potter: MOR occurs to me: Always be sure you know exactly what you are both talking about. I may well be missing Eliezer's real message.
If you genuinely think this is a smart thing to do in real life, it makes me seriously worry about your safety and the safety of people around you.
What are we really talking about here? Being as EY may be several levels ahead of me the intended 'this' could be "implying that a respected authority is obviously wrong without a clear benefit to yourself". That would make for extremely good advice, and a valid concern. Fortunately I for most part avoid that in real life. It does cost me and I do limit my options such that my environment doesn't put me in that situation too often. One way to ensure my safety is to not put myself in situations that prompt risk taking. It isn't optimal, except in the bounded sense, but it does work.
Time travel in this universe has a consistent single line; once McGonagall sees Harry disappear, he can't undo it.
Update: Please post new comments in the latest HPMOR discussion thread, now in the discussion section, since this thread and its first few successors have grown unwieldy (direct links: two, three, four, five, six, seven).
As many of you already know, Eliezer Yudkowsky is writing a Harry Potter fanfic, Harry Potter and the Methods of Rationality, starring a rationalist Harry Potter with ambitions to transform the world by bringing the rationalist/scientific method to magic. But of course a more powerful Potter requires a more challenging wizarding world, and ... well, you can see for yourself how that plays out.
This thread is for discussion of anything related to the story, including insights, confusions, questions, speculation, jokes, discussion of rationality issues raised in the story, attempts at fanfic spinoffs, comments about related fanfictions, and meta-discussion about the fact that Eliezer Yudkowsky is writing Harry Potter fan-fiction (presumably as a means of raising the sanity waterline).
I'm making this a top-level post to create a centralized location for that discussion, since I'm guessing people have things to say (I know I do) and there isn't a great place to put them. fanfiction.net has a different set of users (plus no threading or karma), the main discussion here has been in an old open thread which has petered out and is already near the unwieldy size that would call for a top-level post, and we've had discussions come up in a few other places. So let's have that discussion here.
Comments here will obviously be full of spoilers, and I don't think it makes sense to rot13 the whole thread, so consider this a spoiler warning: this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series. Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.
A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted. This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.