Would a dedicated carrier build be best?
If you are trying to get some flush deck aircraft carriers in service during World War One you're better off accelerating Argus, Eagle, Hermes and Vindictive.
IIRC one of the things that delayed them was that the projected date for the end of the war was always before the expected completion date, which became a self-fulfilling prophecy.
If I was you I'd also modify Hermes by putting a maximum speed of at least 30 knots in the staff requirement. Do that by doubling the installed horsepower from 40,000shp to 80,000shp. A larger hull will be needed, but that will have the advantage of a longer flight deck and larger hangar.
The earlier start would also make it easier to do a more thorough conversion of Vindictive or even better build a second ALT-Hermes.
If you want a POD I suggest 1909 when the Committee of Imperial Defence decided to discontinue work on aeroplanes and concentrate on airships initiating the saga that ended with the R.101 blowing up. It effectively put the development of heavier than air military and naval aviation by 2 years because the Air Battalion, Royal Engineers was formed in 1911 and the first quartet of naval pilots were trained in 1911 also.
IIRC Lord Esher initially agreed with the decision, but after seeing the rapid advances that took place changed his mind and pressed for the purchase of 40-50 aeroplanes for evaluation.
That way you could have the training of the first pilots, the Africa/Hibernia/London trials of 1912, the Hermes trials and the purchase of Ark Royal (or a ship like her) brought forward by 2 years. Campania might be purchased 2 years earlier too. The earlier start might be enough time for the OTL Beardmore aircraft carrier that was being designed before World War One to evolve into the ALT-Hermes.