The best time for planning a book is while you're doing the dishes.
I'm just going out to test whether this theory applies to mowing the lawn.
Later - I can faithfully report that the only creative thoughts that entered my head while mowing were of revenge against the person who laid shell paths in the garden: it has never been a decent mulch, murder on bare feet, and spreads through the grass to become deadly shrapnel when the mower hits. I think I maimed one of the chooks.
I can also attest that unblocking the composting toilet for the fourth time in as many months doesn't do much for the creative process either.
I'm going to try baking banana bread instead.