The letter arrived yesterday.

So what, eh? Letters arrive all the time, usually delivered by Andy, an older man with a limp and a lisp and an ever-present smile. The post the postman usually posts consists of bills, but even they are fast becoming an online only experience, thankfully. It's easier to delete an email than have to ignore an impatiently waiting envelope. I wonder if the internet is doing poor Andy out of a job. Maybe that's why junk mail and flyers have been replacing actually useful deliveries.

This particular letter hadn't been ignored, even though it remained unopened. No, it stared at me, willing me to pick it up and tear it open, revealing the textual treasures within. So, why was I yet to do so? Why was I so reticent about doing something so mundane?

Well, because yes, it had arrived yesterday, but it had been sent tomorrow.

In fact, in true apocalyptic movie fashion, the day after tomorrow. Overmorrow, a word I'd never used before but always wanted to and probably never would again. Now, forgive me if I'm mistaken, but wouldn't that concern you?

Possibly not. Probably not. It was a misprint on the postmark thingy automatically stamped by the miracle that is modern technology. That was all. A glitch in the matrix I don't believe we exist within. You know, some people do believe that? They are probably the same ones who think the Earth is flat, and it should be a globe but is the Matrix buffering.

So, yeah. It could be a mistake. These things happen, though I'd yet to see one such as this. The cogs in the Royal Mail machine may go extremely awry on occasion, but this would be an automatically updated function. Andy's mate Mike – such a common name – wasn't sitting there in his office, his only duty to type in 'today's' date once midnight passed. What would he do in the long hours between? Wish he had a more interesting name?

No, mistakes happen, but not this, at least, not on this day.

The letter arrived yesterday, handed to me personally by Andy due to the parcel he was also bringing, which wouldn't fit through the letter box. Thankfully, he was conscientious enough to not leave packages in the plain sight of would be thieves, then scarper before my dogs had the chance to bark their warning of a visitor. As I was more interested in the parcel, I merely glanced at the envelope before dropping it on the dining room table, repository for all non urgent things. I did see it was addressed to me. I did see notice the handwriting, and it did strike me as odd. And my eyes did catch the impossible date. But, the shiny new item in the cardboard box shoved such things aside, wanting to be the only object my brain was interested in.

It was a switch. Shiny, brass and simple, though ever so important. It was the finishing touch to my device. The cherry – not that I like the fruit – on top of my electronic pie. As I fitted it, I was excited. Sweating, a little. Breathing heavier than usual. This was it. After what felt like a lifetime and a half of full cream dairy labour, I'd completed my masterpiece.

It was unassuming, but beyond powerful. To say its name was to diminish its glory, mainly because it sounded cliched. If you invented a time machine, wouldn't you feel the same?

Of course, I didn't know if it would work, but then, perhaps I did, and that's what made me nervous. You see, along the way, I'd written some rules. Whether the butterfly effect was real or Time was resolute, I was yet to discover. However, I would do nothing – or as little as possible – to affect any changes. I certainly would not send myself a message from the future. We've all seen how that worked in the movies. Marty McFly I was not going to be. Besides, I couldn't play guitar.

My finger is poised over the switch, but my attention is on the letter. It arrived yesterday, but it's dated tomorrow. And the handwriting is my own.