The world of internet would be a _much_ better place if everyone at least have read this. I tried my best to adhere to these rules in any social network.
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I've sent a lot of HN mod mail over the years, and usually get a response within a few hours. Occasionally a few days, during busy times, and on a very small handful of instances, an apology for missing or overlooking an email. I think all of those have occurred within 1--2 weeks tops.
I try to keep most correspondence short, sweet, single-focused, and direct. (Most of that concerns submissions: titles, URLs, or nominations to the 2nd chance pool.)
Occasionally I address more complex or difficult issues. Dang emailed me a few days ago noting that he's still meaning to reply to series on one topic (not pressing, though interesting). I'm aware that he's pressed and that there are more urgent priorities. But he does go out of his way to stay on top of things.
(I also owe him a reminder on another issue, also fairly minor, I'd raised a couple of months back.)
Keep in mind that mods are ingesting a firehose and that complicated or poorly-scoped questions or issues might be difficult to respond to. (This is a general principle to keep in mind when corresponding, not just for HN mods.)