While I agree, that would be really great to have, with the current engine, it's not possible.
Many things in the engine use days for their takt. For example, loss and gain of cohesion is calculated daily for each element(!!)--yes, kids, don't try this at home
But unfortunately, some parameters use turns as their takt. When creating a new game, Pocus and the devs have to tweak the AGE game engine, so that these parameters fit to the days-per-turn paradigm of the game. So changing the days-per-turn within a game with the current engine is unfortunately not possible.