Emett has been rising at 6am to fit in training, mostly near his East Auckland home, before heading to his Britomart restaurant, Ostro.
But he has also trained on sections of the event course while in Queenstown to oversee his restaurants Rata and Madam Woo. He boasts he's the "perfect student" for his marathon trainer Gaz Brown.
"He expected to see me miss all these sessions. But I've run exactly what he tells me," Emett said.
Brown has been impressed, "considering he comes from a profession that stereotypically does not see a lot of exercise".
Emett has, however, struggled to eat to keep up with his energy output. He has introduced protein shakes and "big breakfasts" like eggs and avocado on toast.
He ran the New York Marathon in 2009 to help a deaf runner "on bugger-all training" and suffered "for weeks" afterwards with tired legs.
This time he has trained hard by doing two strength classes and running four times a week to aim for a 3hr 45min race time.
His mum will cheer him on, and his wife Helen will run the 10km course on the day. They will celebrate at Rata with friends.
Marathon chief executive and race director Dave Beeche believes entrants were drawn to the stunning scenery, including a backdrop of The Remarkables, Arrowtown, Lake Hayes, Lake Wakatipu and Queenstown Gardens.