How long does it take an apple to brown, out of water and soaked in water?

Note these factors:

Excess or too low humidity can have a detrimental effect on fruit during storage. If the humidity is too high, the cells swell and expand to the point where the tissue cracks. Too low humidity causes dehydration of the tissues leading to shriveling. I would point you also to the site below, it records a wealth of physiological disorders affecting apples:

http://tfrec.cahnrs.wsu.edu/postharvest-export/physiological-disorders/

Apple slices - a trademark of school lunches everywhere - typically turn brown and soft in just a few hours. There is no fixed time limit on precisely when the fruit will begin to brown. Fluctuations in the variables affecting oxidization will mean that "browning" occurs at different times. Fresh cut apples turn brown when iron-containing chemicals inside apple cells react with oxygen in the air. We see this every day when iron objects rust, or when scabs on cuts turn brown. The chemical reaction is called "oxidation", and the enzyme that regulates oxidation in apples is called "polyphenol oxidase" (PPO), also known as "tyrosinase". There are millions of tiny cells inside each apple. One way apple cells get exposed to oxygen is by cutting the apple open. This damages the wall that protects each cell and exposes its contents to oxygen in the air.

Bruised apples also exhibit oxidation. When an apple gets damaged--as might happen if it were dropped--many of the cell walls inside the apple get broken. This enables the contents of those cells to flow freely inside the apple, where they react with air that is also inside the apple (apples are 20% air--that's why they float). The easiest way to keep your sliced apples from turning brown is to keep them in a bowl of water. If you are placing your apples on a serving dish, you can brush them with water that has a small amount of lemon juice added to it.

http://foodpreservation.lifetips.com/faq/118305/0/how-do-you-keep-sliced-apples-from-turning-brown/index.html