Quote Originally Posted by tolis View Post
We know that unstressed O sounds like A and unstressed E sounds like И.

My question is does this situation occurs on the syllables before the stressed one or into the whole word?
In the whole word (unless the word is very long and there is something like second stress).

Quote Originally Posted by tolis View Post
and second, are they any exceptions in that rule?
Well... This is a problem of articulation, not of some formal rules. I'd say that in fact all unstressed vowels in Russian are pronounced as schwa, unless speaker exaggerates articulation. In normal speech Russians used to hear А and И, but foreigners (as this forum shows) can hear something rather unexpected instead.