For most students, ten to twenty. The number that matters is not how many you can write in an evening but how many reviews you are willing to do every day for the next two months.
A new card is not one review. It is a review tomorrow, another three days later, another the week after, and a thinning tail for months. Twenty new cards a day settles into something like a hundred and fifty reviews a day once the schedule fills out. Fifty new cards a day becomes a part-time job by week three, and the usual outcome is not a well-reviewed deck but an abandoned one.
The fix is to stop adding new cards for a week rather than to reset anything. The count falls on its own as intervals stretch.
Ten well-written cards outperform forty vague ones, and they cost less every day afterwards. One idea per card, a question with exactly one answer. A card that keeps failing is a card that keeps costing you reviews.
There is no daily cap in Reps. The restraint has to come from you, and the seven-day chart records whether you managed it.
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