I'll be back in a tick!
It'll just take a tick.
I'll only be a tick.
These three phrases refer to a tick as an amount of time. This entry will illustrate three different lengths of time that a tick can represent, and will hopefully answer the question - how long is a tick?
Length One - a Tick Is One Second Long
The dictionary defines a tick as 'a light recurring click or beat, as of a clock or watch'. Since on a watch or clock a tick is one second, by following the dictionary meaning, this must be the value of a tick. However, the dictionary meaning does not refer to a tick as a length of time in any meaning, apart from as a click or beat. What the dictionary does do is suggest that one second is the length of time of a tick, as it mentions the click of clocks and watches where one tick equals one second.
Length Two - a Tick Is Equal to a Tock, or Half a 'Tick-Tock'
Since on an old clock the length of a tick and a tock are the same, a tick must therefore be equal to a tock, or half of a 'tick-tock'. Although this length, is derived from the passage of time on a clock, it is also derived from the human internal keeping of time. Keeping time by counting 'tick-tock' gives humans an accurate way of measuring time equally. It would be much harder for humans to try and keep time in minutes without a watch or clock.
Length Three - a Tick Can Be a Short, Varying Period of Time
This definition comes from the phrases at beginning of this entry in which a tick represents a short measurement of time. The first two lengths of time were very short and that is because a tick is a very short length of time. However, this third definition, although short, is more open to interpretation, and is definitely a lot longer then the other two. This is because of how it is used by people. When someone says 'I'll only be a tick', what they are really saying is 'I won't be long'. The former is more positive, and sounds better than the latter. In this way, a tick can be used as a short value of time to make a sentence sound more positive.
According to Merriam-Webster's Online Dictionary, one of the many definitions of a tick is:
... the time taken by the tick of a clock: (MOMENT)
A moment is 'a short space of time' so this definition seems to support Length Three - that a tick is a short length of time.