About 30s to 90s each. Less for compound vocab, more for kanji.
I drained the queue in one or two sittings until level 9, at which point I realised that the large blocks of reviews I was building (sometimes over 250 at once) could effectively be split by doing twenty reviews, hitting the home icon in the top left (or the wrap-up button, which I didn’t notice at all), then doing another twenty the next hour and so forth, breaking down the spikes.
Now I just do five lessons per hour from when I wake up until noon, clearing the less-than-two-minutes-long five-review pockets every hour until I get home, and break down any spikes in the evening to try to maintain about 15 to 20 reviews per hour until 23:00 (the second review session from the noon batch), then the cycle repeats the next day. Anything I got wrong during the day will get kicked out of the cycle and be waiting in the morning, when I’m rested, which has helped me to eliminate all leeches.
Takes about nine days per level this way, but I’ve had no trouble maintaining the pace, and if I miss a review-block due to a meeting or something, it just leaves a very manageable ten waiting.
