Single word for a very small amount of time [closed]

A blink of an eye and a split second come to mind.

Edit: If you insist on a single word, you'll have to go with an instant, or get creative and change the sentence structure to accommodate a different part of speech, like momentar(il)y.

One can take a moment or an instant to indicate a short amount of time; depending on context this may mean a fraction of a second, several minutes, or a period of years:

The doctor will be out in a moment.

Neo-swing enjoyed a moment of mainstream popularity in the 1990s.

Something which is almost instantaneous is done in a flash, blink, or twinkle, by metaphor to a lighthouse, eye, or star respectively. I would consider these words too informal to use in business or technical settings, however. Even more casual is jiffy or jiff, which I would only use in very familiar settings or to children: Don't cry, little girl, your mommy will be here in a jiffy.

If the amount of time will not vary, I might suggest tick, representing the smallest movement of a clock, but undefined. Of course, there is a risk that tick could be misinterpreted as a literal second or a minute. In spoken language, conversely, second or minute do not always represent literal amounts of time; I'll be back in a second or It'll take a minute to get there simply mean a short time. This is extended further in expressions such as the five-minute rule or fifteen minutes of fame.

As noted in various comments, these terms may have specific definitions within certain domains, for example moment, jiffy, tick, instant, and shake on the small scale, and terms like age, era, eon, epoch, and so on at macro scales. Take appropriate care. Of course, no matter how short a time is involved, you'll have someone complaining that it takes forever.

I would say they are colloquial, but I have always like tad or mite