Question: I've read a post on this topic, but really not sure of the difference when applied to something like this:

> 
> 私は朝飯のみ**に**茶を飲む  
> 
>  私は朝飯のみ**で**茶を飲む
> 
> 
> 

From what I read, I'm guessing one of them is incorrect, as に is used for specific times and で　for ranges of time in which an action happened. So I'm guessing に is the incorrect one. Could someone confirm me this please?

Answer: 
Both means *today*, but the meaning depends on the pronunciation.

きょう refers to the day after yesterday, the day before tomorrow.

> 
> 今日【きょう】は雨【あめ】が降【ふ】っています。 It's raining today.
> 
> 
> 

こんにち means *present age*, *nowadays*, or *these days*.

> 
> 今日【こんにち】の若者【わかもの】は新聞【しんぶん】を読【よ】まない。 Young people of today do not read newspapers.
> 
> 
> 

This difference is rather strict; basically you can't expect they're interchangeable. I recommend that you memorize how to use きょう first, because こんにち is less common.
To see that 今日{きょう} is a special reading, you need to look in a kanji dictionary. 

[「きょ」 is not listed as a possible reading of 「今」.](http://jisho.org/kanji/details/%E4%BB%8A)  

[「う」 is not listed as a possible reading of 「日」.](http://jisho.org/kanji/details/%E6%97%A5)

「今日」 is a 熟字訓{じゅくじくん} which is best explained [in the wikipedia entry for "kanji".](https://en.wikipedia.org/wiki/Kanji#Special_readings)