The only thing that comes to mind is Fischer's statement: "...Averbakh found a hole in my analysis with 20 B - B6!...I spent an evening just staring at the position after 14 QR - Q1, trying everything, unwilling to let my brilliancy go down the drain." (Note to 14 KR - Q1? in R. Byrne - Fischer [Game 48: The Brilliancy Prize], on page 299 of the 1969 Edition).
There may well be similar comments elsewhere, though I'm not aware of them.
The book has never struck me as having a particularly light analysis; it seems on par with books like The Life and Games of Mikhail Tal or the OMGP series and far surpasses Bronstein's book on the Zurich Candidates'. Certainly, not all games or comments are the same, but that's how all books are.
This is just brilliant and I am so happy you found this for me.
Do you think it tells us on his method and philosophy of personal game analysis?
Did he analyze in order to diagnose his weaknesses or did he analyze in order to develop his chess understanding? Or both?
I don't know the meta here, I am getting the gist you are finding it hard to believe. And that's why most others are describing to you what it means to be a chess pro. The analysis and synthesis, the abstract and concrete, have to be in balance. I don't know the ratio but from my experience 50-50 is best.
To your question, I do know that with SuperGMs and in particular those whose life goal is to be world champion, the mind will direct all thought activity to chess.
This is the case with Magnus and from what I have seen from Fischer, this was the case with him also. They even refrain from sleeping sometimes, just lay down eyes closed and go over chess positions until sunrise. And only the body rests.
So yes, they will have taken it as far as analyzing games for days. Because they want to achieve a level of brilliancy they're not yet familiar enough with. And also, that's why they will have 0 interest in playing common professionals, amateurs, or other forms of commoners. What else is there to do but prep and analyze until the next tourney. That's how they work.