So, while revising to my Eddison piece I came across a striking passage that I'd either overlooked before or, more likely, read when the book in question (Paul Thomas's edition of ERE's ZIMIAMVIA) came out (in 1992) and since forgot.
In a passage discussing the composition of THE MEZENIAN GATE, Paul describes how Eddison wrote slowly but persistently, writing and rewriting a passage until he was satisfied with it.* By Paul's estimation, at times, when working on particularly important passages, Eddison wrote an average of about twenty-five words a day.
Even given the amount of time and energy the War took up during Eddison's final years, that's punishingly slow progress, especially for someone who had taken an early retirement in order to devote whatever time he had left to his books.** It's surprising he got as much down of that final book as he did, and testimony to his persistence.
--at the desk, with Hastur in a box, on the desk, soaking up warm bright lights and accepting a little handheld bowl of water.
*ZIMIANVIA p. 572-573.
This is the exact opposite of Dunsany's practice: Lord D. made it a point of honor never to revise his work but to present it just as he had left it once he'd captured the idea in words.
**Eddison walked away from a senior post at the Board of Trade (including, it's said, a probable knighthood); I'm not certain of the date, but it seems to have been about 1939 (with his sudden death coming in 1945).