Hello! Hmmm... I'm sorry... I'm not sure your question. I considered the meaning of your question.... Maybe... Do you want to know the difference between "今日” and "こんにちは"? If you want it I will be able to answer to you for the meaning of them.
今日: This word has two pronunciations and has subtly different meanings.
Pronunciation 1: Kyo(long o): Meaning Today.
Pronunciation 2: Kon ni chi: Meaning In recent years, modern, present, means the present moment, now. This word is used in news reports, presentations such as academic societies, papers, etc., and it is a commonly known word, but it is not used as a spoken word in everyday life.
こんにちは: Pronunciation: Kon ni chi wa: Meaning Hello, Hi
It is a very common greeting. The exact meaning is, it is a greeting used from noon to evening. However, the Japanese generally use that word from around 10:00 in the morning until sunset.