Your phrase means "good morning/good afternoon" (as you know) but can also be used as a greeting like "hello" in English. The translation into Nepali is "Namaste" (hello) if you wish to use it like a greeting but if you specifically want to say "good morning" the formal form is "Subha Prabhat". I knew the "namaste" phrase but had to look up the phrase for "good morning". See the reference below, it's from the book "Insight Guide to Nepal" pg 354. HTH.