Not at all in stone, Theres some variation in the dates, and I can halt naval production or accelerate it, for each ship, if they are already being built(hull laid, not before that, though). Ships can also receive upgrades in weapons, systems, armor etc, I can choose between the upgrade or whether to upgrade them at all. For bigger ships each upgrade might mean a month in the drydock. Upgrades are mostly historical ones for the ship class in question, but there are also a couple of what ifs.
Aircraft industry is completely "free" for Japan, including research & design. Ground units' reinforcements depends on where they are, how well supplied, administrated and where the HQ they have been assigned to is. I can also effect pilot training and who is assigned to what squad, depending on their skills and branch, of course. There is quite a complex industry system that uses different resources, refineries and factories to create supply, fuel, weapons, engine, aircraft, ships as well as repairing at drydocks... All that stuff has to be moved around the map too, there are just 2 off-map pools, for 6 resources. That means I have to run huge convoys that bring stuff from China and later Dutch East Indies to keep my home islands' industry running. On the returning trip the convoys take supplies and fuel to the front and island bases.
I am not going to make the mistake the real Japan did with pilot training and aircraft design... I already have 4 fighter and 3 bomber schools set up, for the lower skilled, but already "graduated", pilots.
There are so called victory points counted for destroyed enemy ships, ground units and aircraft, as well as possessing bases/areas as well as having units. If by January 1st I have enough points, the game will end as the Amis will give up and suggest a peace treaty. If I dont, I can try again in Jan 44, but that is going to be though... By late 1944 the Allies should have total dominance of the seas. They can easily outproduce the Japan.