How long is a 'wink'?

If I'm off to catch forty winks, how long will I be asleep?

I'm interested to know if there is a specific amount of time associated with a 'wink', or if there's no actual amount of time behind it?

"Forty winks" is just an idiom meaning a nap for a short period of time. From the Wikipedia entry:

To take forty winks is to take a nap for a short period of time (usually not in bed), or to take a short sleep during the day. The term Forty winks is an English idiomatic noun that can be used in the singular or plural. This can be used in sayings such as "Tom had 40 winks during his dinner hour, while Brett was busy at work".

Alternative idiomatic sayings such as could not sleep a wink provide the mental picture of a wink being the shortest type of sleep available and "forty winks" therefore gives an indication of an appropriate short sleep.

A wink is a very short period of time, a moment; also known as "the blink of an eye" (as in "quick as a wink"). Other languages have this expression as well. Cf. German ein Augenblick, etc.

A wink is much longer than a jiffy and about the same time as a single shake of a lamb's tail.

In his final (and incompleted) novel, The Mystery of Edwin Drood, 1870, Charles Dickens quantified (or had his character Durdles quantify) a wink as a second long. How a nap can be 40 seconds long, I do not know. Perhaps it refers to the actual time it takes a very tired person to fall asleep.

According to Wikipedia a blink lasts for 300-400 milliseconds; if we postulate that a one-eyed wink lasts the same amount of time as a two-eyed blink the duration of a "40 winks" nap would be a staggering 12-16 seconds. However, a wink is technically half of a blink so if you're off for one now to sleep off the knowledgeficating effects of this thread you can probably allow yourself a sly seven seconds. Oh go on then, make it eight. Treat yourself. Wink wink.