The most common greeting in Arabic is the phrase “as-salaamu Aalaykum” which means literally “may peace be upon you”. And the most common reply is “wa Aalaykum as-salaam“, which means literally “and upon you peace”.
But as you see in the above phrases, to learn a language, you have to learn its culture, because literal or direct translation doesn’t make sense when you speak that language.
The same thing in “SabaaH el-khayr” = good morning, and the response of it, which is “Sabaah en-nuur” while “nuur” means literally ” light”, but this is the way how Arabs greet each others, simply means: if you greet me using good words, so I have to greet you using better words!.
Also there is no specific word for greeting in the afternoon. You can use simply either “as-salaamu Aalaykum” at anytime, or “masaa’ el-khayr” for the afternoon as well.
Take the in here to learn more about (Arabic Greetings)