"Training hasn't been as good as previous years in terms of kilometres I have been running. I used to be running 200km a week but that has dropped to 130-140km, which is enough to stay fit but maybe not enough to do a really quick time.
"I have been doing my master's degree and working a lot and I have a young daughter, which takes a bit more time than usual so fitting it all in is a bit more challenging.
"I am a bit unsure compared to previous years around how my body will respond."
While considered an outside threat to win the race, 32-year-old Lett has identified three other runners to fight out for the men's title.
"I know there are some really fit guys around the Auckland scene at the moment," he explains.
"There is an Irish guy Ciaran Faherty, there is a guy in Wellington, Nick Horspool, and a guy from Auckland, Tony Payne, and I know those boys are really fit and have done quite a bit more work than I have."
The Rotorua course, which sees competitors start in the downtown area of the city and completely circle Lake Rotorua, is steeper than many other marathons around New Zealand and has become one of the iconic races on the calendar.
"From previous years I know the times are a little bit slower than in other courses which are flatter," Lett says.
"It has been around a really long time and has some history of who has won it. It is a bit of a who's who of New Zealand marathon running really."
The leading female runners are Mel Aitken of Dunedin, Klaartje van Schie from Palmerston North and Auckland's Katie Wyrill.
Former Olympian and previous winner Liza Hunter-Galvan also lines up again.
The race begins at 8am with runner's contesting the full marathon beginning 20 minutes after the half marathon runners.