To answer the question, there's really two time scales involved in the Campaign Series games.
First, there's what I call the game basis time scale, how units are designed, which old Talonsoft manuals stated to be 6 minutes but what I have intepreted to be closer to say 10 minutes on average. This is what needs to be considered when designing new units into the game.
Then, there's the scenario time scale, ie. how many turns does it take to cover a certain battle, where it all really depends on the action depicted. As the game play cuts typically all slack time off, as players keep going at their targets, a 30 turn scenario can equally depict a day worth of slower action, or just a few hours of hectic say meeting engagement action. This (number of turns for a scenario) is what needs to be considered when designing a scenario. Typically, even then it takes a few test plays to figure out the optimal scenario length for the action covered.
That's how I view this anyhow