Wehll the 15" barrels will not be needed..... Yet..... Dunno.....
Anywho,
If all the secondaries need replacing that is cool. I forgot the 5.9" were cruiser and destroyer guns as well. I was thinking WW2 & 8"! lol
The new turrets..... Pity they can't be taken from the Nassau Class but they were the same turrets as the Von der Tann. No doubt parts could be approprated but not whole turrets.
So 2-ish months for new turrets. Barrels can be swapped in as required. Secondarys swapped in as required.
Armor is custom to a class so that may take time. Propellor shaft..... mmm Pull one out of the Mackensteins or other 2 Bayerns? Possible I suppose. I doubt that BCs would be THAT much different between classes on the actual propellor shaft. The propellor is fine so are the engines. It is just a swap out there really.
Would three months be satisfactory to get those four ships 100% fully operational again? Mid to end of June for the last one?
Damagerepair depends on the extend of the damage. Propulsiondamage is far more difficult to fix, than damage on the outer parts of both hull and fittings, such as armament. A damaged shaft is only to be repaired, when the entire hull is opened, as is the damage or replacing of engines and boilers. With the presence of deckarmor, opening a ships hull is quite complex and done only when absolutley needed.
Most damage to the OTL Juttland battleships of the Hochsee Flotte was rather supervisual and limmited to mainly the outer layers of the ship, while propulsion was not basically affected. (appart from Lützow, which is why she was scuttled as she could not get fast enough to get clear of the action.) So most of the damage was repaired quite quickly, also because the docks at Wilhelmshaven were quite advanced and realy good equipped for the job. (at that time at least.) Portsmouth in the UK too was equaly up to this job, but most other dockyards were less advanced, so depending on where a ship went made a lot of difference.