Training that requires a high level of concentration, detail, and /or repetition is the mental equivalent of high intensity exercise.
As such, my recommendation is doing shorter rounds, increasing or decreasing duration based on diminishing returns. That is, if your focus starts to slip, back off next time. If it’s too easy, make it more challenging.
In general, push for slight discomfort, keeping in mind that severe discomfort over time will decrease enjoyment and lead to burnout. Make things sustainable, understanding there is a process involved. Slower is faster, especially in the long-term.
Taking blogging for example, I used to only blog several times a week, as that many ideas was a stretch for me at the time. Now I could probably do three posts a day if I wanted. The broader point is this was akin to building a mental muscle over time (compare that mindset to the practitioner who’s constantly on the lookout for the ‘better shortcuts’ lol).