Ohayo or Konnichiwa, Which Would Japanese Use?
As you know, Ohayo (おはよう: also spelled Ohayou) and Konnichiwa (こんにちわ) are commonly used Japanese phrases for greetings, respectively meaning Morning and Hello or Good Afternoon.
While Konnichiwa is usable with anyone, only Ohayo sounds casual, so we usually add ございます to make it polite/formal, and Ohayo Gozaimasu (おはようございます) is the expression for Good Morning in English.
Ohayo vs. Konnichiwa
Japanese people usually say Ohayo (Pronunciation) to family members after waking up. And when seeing neighbors outside, they would say Ohayo Gozaimasu (Pronunciation) in the morning and Konnichiwa (Pronunciation) in the afternoon.
But how is it going with friends, store clerks, in the office, and business?
In the case of meeting with friends, we may say おはよう/Ohayo in the morning, but we never use こんにちわ/Konnichiwa at any time.
Instead, we would say, depending on the situation, 遅れてごめん/Sorry for being late or 結構待った?/Did you wait a lot?
With Store Clerks
In the case of shopping at stores, clerks usually say Irasshaimase (いらっしゃいませ, meaning Welcome) to you, and they may add おはようございます to it in the morning at opening time.
Many customers don’t return a greeting, but you can reciprocate Ohayo Gozaimasu. In the afternoon, store clerks would only say いらっしゃいませ (they usually don’t use Konnichiwa).
In the office
When arriving at work in the morning, we usually say おはようございます, and in the afternoon too, many companies demand employees to use Ohayo Gozaimasu.
The same thing also applies to the night shift, and they would say おはようございます even at midnight after coming into the office.
When Japanese meets with clients or business partners, we would say Ohayo Gozaimasu in the morning, but we usually don’t use Konnichiwa at any time.
Instead, we would say Otsukaresama Desu (お疲れ様です, translated as Thank you for your work).
(Reference Page: Tenshoku Restaurants )