Correct, mrC. they never are, its a game, not a simulation.
The turns, movements and units are all very abstract, and its impossible to stick them to any kind of timescale. If you try, you will find that a fast WWII carrier use longer time to cross the Atlantic than a sailing vessel from 1500, and that tanks and trucks from WWII use longer time to drive to Moscow than Napoleons men used to walk there on their feets. A turn represent 6 months in time, but only a days walk in distance, and a unit represent anything from a rifle coy to an armoured corps. Its just abstract, for the fun purpose.
If this game should have any link to the real war, it would need to be designed like World in Flames, the hex and counter game.
-Yoy could say that a turn represent 3 months, and the units you purchase represent what was possible to draft or produce in that time.
- In a summer turn, your units could move like 4 or 5 times. Making an infantry unit move 4 territories in total, and a tank move 10 territories etc. In the summer turn there would also be possible with many rounds of combat for every combat move. So in this turn the units would see much action and take great losses.
-In a winter turn, the land units could only move like one space, and only have one round of combat.
So if units, turns and movement get fixed numbers, then you could make a rational timeline. But not as it is