People mark the passing of time in different ways – some by crying, others by ignoring it completely. I like to take something of a methodical, historicist approach and work my way backwards, like Tony Robinson on an archaeological dig.
First of all I work out what I was doing a week ago, then two, then three, then all the way back to 17, perhaps; sometimes I do it in years. It works well during long car journeys or revision sessions. When I was 17 and doing my A-levels, I could tell you exactly what I had done every Friday night for the previous two years. Obsessive? Perhaps a little bit, but I like the fact I can remember almost every pub I have ever been in. If only I could remember leaving them.
Recently, though, I've been thinking a lot about what a difference a day makes: 24 little hours, and all that jazz. It's the difference between waking up with a hangover that would have debilitated even Goliath himself, and waking up feeling human again the next day. You'd never think that a liver or head which felt as if it had been jumped up and down on could recover in such a short time, nor that a mood based on the impending sense of the sky falling on one's head could clear up so quickly.
A day, in fact, is the perfect amount of time to make you feel grateful for your health; as soon as you're under the weather you rue the elasticity of modern life – that it should so test your physique to such extremes – and you become amazed that the human body snaps only even half as often as it does. This sort of profound thinking usually happens on the sofa, in front of a five-hour marathon of (if things are really bad) Come Dine With Me or (if you're seeking moral absolution) Jamie's 30-Minute Meals.
A day feels an interminably long stretch of time to crawl around feeling sorry for yourself and clinging to the toilet bowl, but once it's over and you're able to stand up again without mewing, it's as if nothing had ever happened. Except for the awed and reverent little voice in the back of your head intoning "Isn't it lovely not to feel sick?" over and over again for the whole morning.
And a day in the digital age is no time at all. I'm constantly surprised by the ability to time-travel, pause, delay and relive several hours' worth of banal existence, simply by leaving the Sky box on Live Pause, or by getting on a plane or train elsewhere. Time spent travelling is neither here nor there, so intangible and strange-feeling that you could have been strapped in for 16 hours or 16 minutes – and neither would be that bad, as long as you haven't touched the vacuum-pack food on-board.
A few weeks ago, I felt very keenly the difference a day made when I had to go to Paris for a last-minute news story in the morning, before returning to London, and then going straight home that evening to visit my parents. From their house in Sheffield, we drove up to the town that, until last year, had been home to my grandmother. It's a small former mining community outside Sunderland, and it's about as far as you can get from Paris Fashion Week in 24 hours.
From tiny fondants and macarons and carpets so thick a stilettoed foot sinks in up to the calf, to sausage, egg and chips and the sort of linoleum you only ever see in health-and-safety videos; from finding my name calligraphied on blotting paper and tied with silk ribbon, and a tiny chair that I was convinced I might break (who cares that they wrote "Monsieur Harriet Walker") to a greasy-spoon lavatory with a plastic toilet seat decorated, inexplicably, with little smiling cartoon puppies.
My inner obsessive calculated that the last time I had been in this café had been four years, five months and 19 days ago, with my Nana. And I had had exactly the same meal then, too. In a bid to appear slightly more soignée this time round, I specified that I wanted gravy on my chips, but not on my egg or my sausage.
"I'll have to charge you for a sausage-and-egg bap," said the waitress gravely, "and then bring you your chips and gravy separately." I told her this would be a fine resolution to a tricky problem. "But you wouldn't get the actual bap," she added.
This was fine too; I wasn't there for the bap. It's reassuring to know that, no matter how much time has passed, or how far you go, or how much you drank last night, there will always be real life – that is, sausage and egg and chips, with or without the gravy.