When you’re doing ultra long hauls flights like 16hrs+, I would recommend using the step climb procedure. This process involves pilots flying at lower cruise altitudes until they burn off enough fuel to climb to the next highest cruise altitude for their route. Here’s an example as to how I would do this route.
So let’s break the flight (Auckland - Doha) into 4 segments/legs (where each leg represents 4 hours)
Leg 1: FL320 / M.84 (Flight Time = 0-4hrs)
Leg 2: FL340 / M.84 (Flight Time = 4-8hrs)
Leg 3: FL360 / M.84 (Flight Time = 8-12hrs)
Leg 4: FL380 / M.84 (Flight Time = 12-16hrs)
What you can see above is that after every 4hrs till I reach Doha, I climb to a higher altitude. What this does is that when the aircraft gets lighter and you proceed to climb, it helps improve the fuel flow and enhance fuel efficiency, hence resulting in a sufficient amount of leftover fuel upon arrival into Doha.
This is how I would do it but you can also break it into however many segments you want. Have fun flying the route @Jerome_Ocena