Wheeee!!! I’m so happy. 
Here’s what I came up with:
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As soon as a card is shown, a timer starts running. It doesn’t appear anywhere on the screen, so there’s no feeling of urgency and I don’t get that instinctive reaction that I have to rush and answer as fast as possible. This way, I can calmly focus on giving a thoughtful response.
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As soon as I flip the card, the timer stops. (I also added tenths of a second, not just full seconds, so that in the future I can fine-tune the intervals based on my reaction time. For example, right now the interval for the “Easy” option is 3 seconds. But if I notice that my answers for easy cards are consistently around 3.1–3.3 seconds — which actually falls into the “Good” range — I’ll increase the interval from 3 to 4 seconds.)
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The next thing I ran into is that sometimes a word has several translation variants. (In my template, it can be up to six.) So the total time to answer naturally increases as well. That’s why I had to set different intervals depending on how many fields are filled in.
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For convenience, I display the timer value at the bottom of the screen. I’ve split that line into four parts, and each value appears right above the corresponding button.
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And finally — I also decided to display markers showing where each interval starts and ends between the blocks. This helps me see whether the current intervals really match this particular card. So for now it’s more of a safeguard to compare the card’s structure (number of filled-in fields) with the corresponding time intervals.
As a result — this little beauty came out of it.
Although for a card with only one field, the time markers at the bottom are different. (3, 10, 17 secs)
Thank you so much for the idea! 