Unfortunately the -not very good RSC adaptation took up her time for about two years, which meant she didn't start writing.
However, a recent 'Day in the Life of' in the Grauniad suggests that once she's on the job, it's not that she's flitting about doing the odd bit of scribbling. 
www.theguardian.com/books/2016/apr/16/hilary-mantel-my-writing-day
I used to be a late starter, but now I get up in the dark like a medieval monk, commit unmediated scribble to a notebook, and go back to bed about six, hoping to sleep for another two hours and to wake slowly and in silence. Random noise, voices in other rooms, get me off to a savage, disorderly start, but if I am left in peace to reach for a pen, I feel through my fingertips what sort of day it is. Days of easy flow generate thousands of words across half a dozen projects – and perhaps new projects. Flow is like a mad party – it goes on till all hours and somebody must clear up afterwards. Stop-start days are not always shorter, are self-conscious and anxiety-ridden, and later turn out to have been productive and useful. I judge in retrospect. On flow days, I have no idea what I’ve written till I read it back. It’s a life with shocks built in.
I don’t mind whether I write by hand or on a keyboard. I don’t mind anything, as long as I’ve woken up calmly in my own time. I’m a long thinker and a fast writer, so most days I don’t spend much time at my desk. I concentrate well. I’m not tempted by the internet. If I’m redrafting, fine-tuning, I print the text and take it away to read it on paper. But if I’m writing straight on to the screen, I tense up till my body locks into a struggling knot. I have to go and stand in a hot shower to unfreeze. I also stand in the shower if I get stuck. I am the cleanest person I know.