1. More formal/direct:
* He aha te wā? (pronounced: hay-ah-tay vah)
2. More conversational:
* Kī atu, he aha te wā? (pronounced: kee ah-too, hay-ah-tay vah)
The second phrase literally translates to "Say, what is the time?". It adds a little politeness and makes the question more casual.
Both phrases are grammatically correct and can be used in different contexts.