Most flights fly to Los Angeles, California from New York. Non-stop flights from New York to Darwin are very rare. So with one stop the approximate time to get to Darwin, Australia would be 19 hours. 5 hours from N.Y to L.A and 14-15 Hours from L.A to Darwin, Australia.
The best time to travel
Many people prefer to travel to the Australian Savanna Biome during the dry season because many of the attractions are open during the dry season. Its also good to go during the dry season because its not too hot and its not too cold.
Clothing to wear
You could wear summer clothing like t-shirts and shorts, but if you go during the early dry season you might have to wear light jackets, sweatpants and long-sleeved shirts.