At some point in my second year my [social science] supervisor told me that it was usually 9 months to a year from seeing a first full draft to submission. I remember thinking, that won't be me, that is an overestimation. She was dead on. From my first shitty draft to final product was a solid 9 months. Perhaps that is because I had a 'big book' thesis which meant that after writing all of my individual chapters I had to spend a substantial amount of time threading my main argument through the whole thing (as well as editing).