I’m not sure the average time spent on each question is of much value. I think the times should be bimodal: ideally, you answer 80% or more of the questions very quickly (at a glance), but you should spend more time reviewing your misses.
Time spent answering a question (vs. reviewing the correct answer when you miss) might be more useful.
“Bimodal” isn’t the whole story though: correct answers for items still in the apprentice stage will take longer than those you’ve already mastered because you will still be relying on mnemonic stories. After several days, weeks, or months of reviews for the same item, it should start to stick into long-term memory and you’ll begin to recognize it instantly.
Similarly, some incorrect answers require quite a bit more time than others as you’ll want to figure out why you couldn’t come up with the correct answer (or keep coming up with the same wrong one). Are you confusing it with another character? Are there any other visual queues you can use to distinguish it from other characters and aid your recall? Can you improve your mnemonic?
You’ll almost always want to spend at least a little time with misses to review the correct answer and try to get it into your head. The only exception really should be characters where you instantly realize that you’ve answered incorrectly for whatever reason (and you already know the correct answer). That should only happen when you’re moving too fast.
Personally, I like to keep my review sessions to under an hour or so, which for me means averaging around 150 reviews each day with 80+% accuracy.
I believe goal of the SRS is to get the items into long-term memory so you can recognize them instantly (at reading speed, without relying on mnemonic stories). IMO this requires missing the answer for items you find difficult so that you will review the harder items more often.
My advice is to almost always answer every question within just a few seconds (without guessing) but when you miss, spend some time reviewing the correct answer before going on to the next question. It’s okay (actually desirable) to occasionally take a bit longer when you think you know the answer but struggle to dredge it from your memory.
Even so, I think it’s a mistake to take too much time answering, no matter what. For me, I’d say 15 seconds or so is the max. If it takes me longer than that, then I don’t know the item, and extra reviews are warranted. I’ve developed the habit of typing “ke”/け for items I can’t answer quickly — it never matches anything. [*1]
Many here seem to think that “efficiency” on WK means few incorrect answers, “perfect” mnemonics, and struggling hard to recall every answer no matter how long it takes. To my mind, that’s exactly backward: the power of an SRS is that it automatically forces more frequent reviews of the items you find most difficult. More frequent reviews only happen if you answer those items incorrectly.
One well-known caveat is that moving too quickly is bad. My biggest irritation is when I start flying through my review session, instantly providing correct answer after correct answer and feeling like a Golden God (“This Japanese stuff is easy!”). Then I answer something I thought I knew incorrectly, seeing a flash of red when I expected green, but accidentally “coasting” into the next question before I can review my mistake. I have to wait for that item to come up again in the same review session before I can figure out what I got wrong. That’s additional mental baggage I could have avoided if I’d just slowed down a bit.
*1: I think I came up with “ke” as a mish-mash of Japanese ゲ like ゲゲゲの鬼太郎 and “Que?” in Spanish — but it’s fast to type and hasn’t matched anything on WK yet!
