I've competed in Nanowrimo several years and could never hit the 50k word (200 pages) benchmark during the 30 days. This took me only ~3hrs a day, with a few longer sprints on weekends.
I updated the prompt every break and made edits. The book is ~90% GPT written, with edits, that will drop to ~70% by word count.
The interesting part for me was that the prompt needed to be updated frequently. I also would rewrite opening texts to cram in the scenes characters and context, so that it could be carried through.