Yeah, 10 minutes/day for 40 new questions/day seemed low to me as well. I agree with you that the plausibility of that figure depends on how long it takes to answer questions.

Matuschak writes:

> In my personal practice, I've accumulated thousands and thousands of questions.

> I spend about ten minutes a day using my memory system. Because these exponential schedules are very efficient, those ten minutes are enough to maintain my memory for thousands of questions, and to allow me to add up to about forty new questions each day.

It takes a while to formulate (and subsequently edit) a single good question (https://www.supermemo.com/en/blog/twenty-rules-of-formulatin...), but suppose we leave that aside and assume that by "using my memory system", Matuschak means answering previously-formulated questions. He says that questions should take only a few seconds each, so suppose it takes 10 seconds on average to answer a question. Then one could answer 40 questions in 400 seconds, which is under 7 minutes. That leaves 3 minutes to review roughly 20 questions of older material.