I once asked a friend of my mother's, a great knitter, just how she managed to be so productive. This was a lady who would typically produce a child's sweater in a couple of days and a complicated aran jumper for a large man in about a week, and she had plenty of other things to do besides knit. What was her secret? "Well, I just always have it on the go," she said to me, "whenever I put the kettle on I'll knit a row, or while I'm waiting for the potatoes to come to the boil I'll do a bit more."
It turns out that there's a fancy name for those 'odd moments' which she filled with activity: interstitial time. I learned this from Oliver Burkeman's highly entertaining and informative book Help!: How to Become Slightly Happier and Get a Bit More Done where, in the 'How to get more done' chapter, there is a brief section called 'Take inspiration from knitters'. Knitting meets the three criteria of a good interstitial-time activity, he says: "it's portable, it can be done amid distractions, and even a few seconds spent on it contributes to the end result. [...] Identify in advance which of your tasks fit the knitting criteria: those involving reading and (hand)writing are a good place to start. Or take up knitting."
Here's a final thought - if you break down your interstitial knitting time into even more fleeting moments, surely that will be 'interstitchial' time?