I am into a trade which is still lasting even after years lol
The life of a trade is purely dependent on the target you will be setting. You may finish off a trade in less than a minute too if you just want to cover exchange fees or even some times under heavy fluctuating scenario, you may get decent profits within that one minute.

No one could exactly predict how long a trade may take. Because the tools we are having will support only price-wise analysis not in terms of time span. Only in speculation we are getting time frames, but they are purely guess-works/based previous similar incidents.