I don't see china need 12 month for see trails even for first ship and it much low tech compare to Aircraft Carrier.
30-36 more unlikely to happen unless somethink defect found. LPH not really an high tech even compare to 055. with just minimum defense weapon on board, out-fitting and sea trials is short of time can complete.
We shall see if the builders take less than 24 months or longer to deliver type 075.
Using lead ship of type 055 is a little off. Lead ship of type 055 has a shorter than expected time to complete her sea trial, probable it was scheduled (during its planning stage) to meet the 70th PLAN navy parade. Which meant it was "rushed" on purpose to meet a specific requirement. Also having delivered more than 10 type 052D, the ship builders, especially JNCX has accumulated vast experience on building DDGs, thus they were able to speed up the work.
LHD or LHA no doubt is less complicated than an aircraft carrier, but they are far more complicated than type 071 LPD, and no less complicated than type 055 despite carried less weapons. At about twice the displacement ( about 40,000 tons) of type 055 DDG, it needs larger power plant , maintenance workshop for helicopters, avionics and engines, aviation fuel tanks pipes and pumps, weapon stores and elevators, aircraft hangars and elevators etc.
LHD/LHA acts as air base for transport and attack helicopters and/or a dock for hovercraft, amphibious vehicles as well as fleet command base for directing a landing operation.
For reference, the vastly experienced American shipyard needed more than 24 months for their lead ships in Tarawa and America class. They are able to cut down the delivery time after gaining experience from construction of the lead ships. The Chinese shipyard has zero experience on LHD/LHA type of ships. (the 20,000 tone type 071 is in different category).
Note that USS Saipan took 39 months from launch to commission.