Formal:
* Kua tae te wā kai tina. (This is the most formal and literal translation)
Informal:
* Wā kai tina tātou! (Let's eat lunch!)
* Kāinga ana te kai tina. (Lunch is ready.)
* Tīmata ana te kai tina. (Lunch is starting.)
If you're asking someone if they're ready for lunch:
* Kāinga ana te kai tina? (Is lunch ready?)
* E hiahia ana koe ki te kai tina? (Do you want to eat lunch?)
If you're talking about a specific time:
* Te rua o te ahiahi te wā kai tina. (Two o'clock is lunchtime.)
* I te wā kai tina. (At lunchtime.)
Remember that Māori is a living language, and the best way to learn how to say something is to ask a fluent speaker.