Can 'on' be used in a temporal setting?

Question

I usually replace upon with on because it sounds less pompous. Is it correct to do so when the meaning is temporal? Consider

Languages change (up)on contacting others.

Should I replace upon with when intead?

Answer 1

ODO indicates that on can indeed refer to points in time.

8. Indicating the day or part of a day during which an event takes place:
reported on September 26
on a very hot evening in July
8.1 At the time of:
she was booed on arriving home

Upon is essentially the same as on, albeit perhaps more formal as you note.

The preposition upon has the same core meaning as the preposition on. However, in modern English upon tends to be restricted to more formal contexts or to established phrases and idioms, as in once upon a time and row upon row of seats. [ODO again]

Generally on denotes a specific time/day or occasion. Whether it's entirely appropriate for something more gradual or process-like such as interaction between languages may be worth considering.

Languages change [up]on contacting others

...says that any contact between two languages will instantaneously change both. If that's not the case — as surely it can't be — an expression which connotes a more drawn-out process might be better than either on or upon.

Answer 2

Try Languages change when they {abut / impinge on / rub up against} each other.

Answer 3

Here on is used with the meaning:

• at the occasion of: on his meetings.

I think on is appropriate in your sencence. When can be an alternative.