But he also made sure to spend time on his own passions and relationships.
His advice to other students is that "your NCEA results are incredibly important but so are your friend and family relationships and your own passions".
"Only leaning into one facet of your life at high school can be fulfilling but it's important to make the most of everything else in your life while it is there.
"That's the philosophy I go by at least."
Going hard during weekdays meant he always had time in the weekend for friends.
"I tried to make sure I never missed a night with my friends because of my school work and I feel like I more or less achieved that."
He admits the 12 hours a day before exams was "gruelling" but he was able to keep it up until the end of exams after which he "had a nice long rest".
Havelock North High School principal Greg Fenton says the "exceptional" student's achievements are "a tribute to his ability to write strongly on a broad range of topic areas".
He adds that Oscar was also school Dux in 2020 and on the student academic committee in his final year.
At the end of his Year 12 school year, he was also selected to attend the National Rotary Science and Technology Forum at Auckland University.
Outside of the classroom, Greg says he was also "a talented and witty debater" who was a member of the top school debating team for his final two years at the school.
"His work ethic was second-to-none when it came to his study, and he proved to be a great role model to the other students in the school.
"We are incredibly proud of Oscar's achievements as a school, and also proud of the support he received from our committed and talented teaching staff."
The Outstanding Scholar Award will provide him $15,000 over three years which he says is "a massive help" and means he feels more comfortable travelling to the South Island to study.
Oscar will be studying health-science at the University of Otago but is considering changing to a Bachelor of Science with a physics or maths major.