>>24624651>>24624663>>24624706It was in the guidebook that came out with ORAS. I'm having a hard time finding the actual guidebook but if you have it you can find the interview in it. The average Pokémon game has two years or more of development and multiple games are developed at the same time (hence all the A-team and B-team talk you used to see but don't anymore) but in the ORAS guidebook interview they mentioned they only spent one year on the game, also mentioning that this is a shorter dev cycle than usual for Pokémon.
There's the possibility that they started working on Z before ORAS came out in which case it would already have longer than one-year of development but I personally want to make sure of that by them holding off the release longer to ensure quality.