How long would it take to build up the decades of experience that the British and Americans had developed?
Some years, but not 8.
The big navys had experience with carriers operating slow biplanes with small bomb loads and regarded the carriers still as an addition to the battleships, not much more.
The Germans had 1933 almost no experience with modern aircraft and no experience with tanks and a few years later, they were far superior to the french and british opponents.
Their mistake was to build an all singing, all dancing carrier (is this the right expression?), one that could operate without escort ships therefore armed to fight cruisers. This was nonsens. What they then needed the most were carriers to protect their capital ships.
The japanese Navy had such "limited" carriers like the Shoho/Zuiho. Fast enough to keep up with the modern german capital ships, but with limited aircraft capacity.
Such ships could be built/converted until 1937/38 and the crews experienced enough in 1940 to operate some Me 109T and deal with Swordfishs, Skuas or Albacores. And with these lessons, they could start building proper carriers.
But neither Raeder nor Hitler were able to predict what will happen, when newer, faster and much more capable aircraft will be available. But who was in the mid 30ies?