ka lā ʻehia / Pōʻahia
What is the difference? Can they be used interchangeably?
In the old days the Hawaiians thought of a day starting on the previous night-- Something like Saturday evening being counted as Sunday in the Catholic Church. "lā" means day. "Pō" means night. Both 'ehia and 'ahia mean how many-- So either way you are asking: How many days into the week i.e. What day? Anyway, that's my thought.