One of the decisions a game designer must make when developing a new game is what value to assign each terrain type for cost to enter (movement cost). Usually woods terrain gets assigned a movement cost of three but in Shiloh I made woods two movment points to enter. At the same time, I gave infantry a total of 6 movement points to spend each turn and made each turn represent about a half hour.
The battle (and the game) started at 5 AM when Powell's patrol discovers massed Confederate units, which starts off the Rebel attack. At 6 AM the Confederates reach the first Union camps. From 5 AM to 6 AM is three turns, including the 6 AM turn.
When I test played the game, the Confederate units hit the Union camps exactly on the third turn (6 AM).
What this exercise did was confirm that my selection of two as the Movement Cost for woods was correct (most of Shiloh terrain is woods). Otherwise, a higher value would put the first Confederate lines reaching the Union camps later than the historical event. Or rather it confirms the relationship between the three variables: terrain cost to enter, turn game time (half hour), and unit movement allowance. Change any of those variables and the results would not be as historically accurate for gameing purposes.