Q: is the estimated delivery on time?

You can't buy an Apple device from Apple from another country; it does not ship internationally. The time of delivery depends on how you get it from NZ to Arg (whether you get a friend there to send it to you by regular mail or other).

Be careful if you buy a phone from abroad, as some iPhone models are country or continent specific, and certain LTE or 3G bands do not work in your country.

If you're currently in New Zealand, then yes, you will likely have it on the 24th.

Disclaimer: this is an estimated delivery time, so if it takes a day or 2 more, you can't blame Apple for being "late".