Bore Da is "Good Morning" and Hylo would be used for "Hello."

Often Shw Mae (S'mae in some areas especially in the North) is used which is kind of "hi how are you."

You wouldn't use Bore Da in the afternoon or evening, you would use Prynhawn Da (sometimes P'nawn Da) and Noswaith Dda respectively.

Lesson over!

(pron guide - Borer Da, Shoo My, S'my, Prinhown Da, Puhnown Da, Noswyth Tha.)