I've been doing pretty well at sticking to the plan of processing the audiobook files until about 4pm, then switching to thinking about The Potential New Book. I'm 3/4 through the processing of "Invasion" and am hoping to get it out either by the end of January or the start of February.
This stage of the processing is fairly dull - removing breath-sounds and mouth clicks from between words/sentences. It's slow-going, but important for the listening experience. No one want to hear me hauling air or making weird noises! But it's one of those activities that uses a bit of brain, but not so much that I'm not able to think about other stuff.
Consequently, while a fraction of my brain works on the audiofile processing, a chunk of my brain is thinking about The Potential New Book, and as well as giving over the end of the work-day to thinking about it, I'm also getting ideas throughout the day.
I always have a notebook or paper at my side, so I've been scribbling down things as they come to me over the day, then processing them more neatly into the New Notebook once I get to 'playtime'.
I'm not quite at that stage where the ideas are coming so thick and fast that I fear I won't be able to capture them all before they evaporate into the ether (thankfully!), but I can't tell you how much of a relief it is that the ideas are starting to flow!