It has been a whirlwind week for Hartley, who only found out he had the job less than a week ago. He spent last weekend racing for the factory Porsche team in the World Endurance Championship, where he looks odds-on to win a second world sports car title.
Significant media interest and support from back in New Zealand followed the announcement last Saturday that he would become the first Kiwi to race in Formula One since Mike Thackwell in 1984.
"Honestly it has been awesome," Hartley said. "The support back home has been awesome - I don't read everything but from what I have read the support has been huge and I really appreciate it."
While the opportunity is only guaranteed for this weekend's US Grand Prix there appears to be a big chance of securing more drives this year or a permanent seat with the team in 2018.
With that in mind, many have been wondering what his objectives will be in Austin. Pierre Gasly, who Hartley is temporarily replacing finished 14th in his debut with the team a month ago. Hartley comes in from the cold however having not raced in a single-seater since 2012.
"[Toro Rosso] haven't really said," Hartley explained about team expectations. "It came about really quick. They haven't put any expectations down - I'm sure they have some - but I'm trying not to put too many expectations on myself.
"Obviously your main reference is your teammate [Daniil Kvyat] so that is the gauge. I am going to enjoy it - it will have a smile on my face - I am a Formula One driver.
"I think I just need to stop talking about it and go and drive. I'm on the edge of over-thinking it. I am just looking forward to getting in the car on and see how I go in that first session and go from there."
Hartley was just seven when he boldly predicted he would become a Formula One driver, says his dad Bryan.
Hartley's father, a handy racer in his own right, remembers his son announcing at a junior go-kart prize giving that he would one day race in Formula One.
"I had given him a Jean Alesi T-shirt that I had picked up in Australia," Bryan Hartley told the Herald, referring to the former French F1 driver who had a long career with Ferrari.
"He stood there and pulled it out and said he would be like Jean Alesi one day. He had this in mind way back when he was seven. There was a picture that came up recently on Facebook with him standing next to Jean Alesi, with his arm around him, talking about that karting story."
The family will get together in Palmerston North on Monday to watch the race together. "It is going to be a very nervous time. I get very nervous and I drive the race with him."
