It was pretty much like that for me too. The first six months was a lot like shore duty. The next six was shiftwork mostly. Then there is PSA. That is Post-Shakedown Availability. Once the boat is commissioned, sea trials are done, and the first ORSE is over, you go back to the yards to fix whatever didn't work right during the shakedown period. However, this also includes alterations to the ship which were not part of the construction contract. My first ship, the USS Baltimore, (where I arrived just before PSA) got new turbine rotors installed during PSA even though the design problem was identified long before the ship was launched.
A huge part of the ship is already built before the first crewmember arrives, but you will se them welding together hull sections of the next boat. Your main engines will probably be five or ten years old before they ever get rolled with steam. A brand-new submarine is actually a few years old before it is launched, and the larger equipment will be a few years older than that.
It is typical government red tape that boats are required to be built according to the contract, even if the design changes. Sometimes you can get things fixed during construction if you can show that they will be a problem. Never accept anything until the yard makes it right. Once you take the system, even if they promised to fix it, they will not fix it. If they do, it will be at the Navy's expense.
Anyway, during PSA, you will see the yard rip out a whole bunch of brand-new stuff only to replace it with newer stuff. The crew on the Baltimore managed to get some racks in the reactor tunnel replaced with lockers. The lockers were perfect for storing the cans that were in them, they were well-made, operated correctly, and sat flush with the hull frames. Adm. Rickover saw them during his tour. (He toured every new boat) When he toured the next new boat, he remarked that he liked the lockers on the Baltimore better than the racks. So, the Navy made an alteration to the design (called a shipalt) and had lockers built on all 688 class boats at their next availability.
You guessed it. During PSA, the yard ripped out all those perfect lockers and replaced them with the new ones designed by the Navy. They didn't sit flush with the hull frames, the construction was inferior, the materials were inferior, the cans wouldn't all fit into them, the doors were too small, and when you could manage to get one open they popped off instead of swinging on hinges.
It is this sort of thing that just makes you shake your head.
SO, it is very likely that you will become very familiar with all the internal and external details of the boat. You will be able to look into the ballast tanks and stuff. It will be cool.
You will also not be spending a lot of time at sea on that boat. If you can, try to get temporary assignment to operating boats for a month or so. That way, you can get some qualifications done. There are certain things that you have to do at sea, and they will be required to get your dolphins or to qualify on certain watchstations..