Does the amount of time an electronic is exposed to water determine the chances of it being saved?

Say one iPhone is left underwater for 10 minutes, and another is left underwater for 12 hours. Will they both have the same chance of being saved? (I'm talking about drying them out after and so forth).

No.

What makes or breaks the survival of a device that has gotten wet
is whether or not the liquid causes any damage
through either electrical shorting or chemical action
(which are sort of related in many cases)
and the exact parts that are affected.

Since every event of this sort is at least slightly different from any other,
there's no reliable way to predict the outcome.

Altogether, the ONLY way to prevent the destruction of
an electronic device by water or other fluids
is to Keep It Dry At All Times.
Period.

Far worse than ordinary water is anything that has acid in it.
Many soft drinks, fizzy ones in particular, contain phosphoric acid,
which will INSTANTLY destroy the copper circuit traces on a board.

Fruit juices with high acid content --- such as orange, lemon,
or cranberry --- will do it, too, although the process might be slower.

Coffee would be another serious acidic death threat.