Diff pronunciation for identical kanji

In what situation is 昨日 pronounced as sakushitsu and in what situation, kinou? The same goes for明日. When is it pronounced as ashita and when, asu?

Besides that, I find inconsistencies between different sources as to how some numbers should be pronounced (in time, minutes). Some of them are as follows: nibun vs nifun
Ichifun vs ippun
Yonfun vs yonpun

Can someone clarify this matter? Thank you.

In what situation is 昨日 pronounced as sakushitsu and in what situation, kinou?
"Kinou" is commonly used while "sakujitsu" is used only for formal occasions. So, if you use "sakujitsu" to your friends, it sounds very awkward.

The same goes for明日. When is it pronounced as ashita and when, asu?
Actually, 明日 has 3 different pronounciations. "Asu" and "ashita" are both used for "the following day" but "asu" can also be used for "near future." For example, "Asu no Nihon" is not "Japan in the following day" but "Japan in near future." In addition to "asu" and "ashita," 明日 can be read as "myonichi," which is used only for formal occasions like "sakujitsu."

nibun vs nifun
"nibun" is often used in the phrase of "wo nibun suru (divide something into two)" while "nifun" is 2 mins.

Ichifun vs ippun
Yonfun vs yonpun
"ichifun" and "yonfun" do not exist.

Sou ka. Got it now. Thank you very much. =p

yonfun is widely used, though it may not be "correct".

http://www.google.com/search?num=50&hl=ja&lr=lang_ja&q=%E5%9...