My agent of course has other clients. She has a bunch of stuff to deal with in September. So I have a couple weeks more.
So rather than just diving into fixing this series of major changes in the last quarter of the manuscript, I'll have a little more time to plan things out and work through possible alternative plot-lines.
There are those who just sit and write with a bare bones outline and those who carefully design their cast of characters and then set them loose. I used to be more spontaneous as a writer, but in all large projects, like programming an information system or doing scientific research, deliberate design and a clear process are just better.
I will often prototype a few chapters now, see how it's going, and then write it over from the beginning when I have a clearer picture of what is and isn't working, as well as having a large outline that has a series of events and plot threads I may or may not slide in as I write the first real draft.
For this project that got me an offer, I think I wrote about 20,000 words before I restarted. Zeroth drafts are not wasted even if I do not use anything in them--as in programming, they help clarify what I want out of the final product during the specification and design phases.
They can also be useful during revision, for getting another perspective on what I thought were problems and what were positives before.