Two more questions - no reference in the manual.

[JDR Dragoon]

No and no. Darkness/Dusk/Dawn has no influence on the games detection routine when the "diceroll" for detection takes place at the start of the enemy players turn (I don´t know whether the games makes a single roll if a unit is eligible for detection or makes several if more than one enemy unit is within detection range). As for reinforcements, you can deploy them whenever you like, but if you bring them on during a night turn (even if you don´t move them) they will incur fatigue. This is very useful to delay a paradrop in order for it to coincide with the rest of your forces (some might consider this gamey though, since this fine-tuning of a units arrival on a turn by turn basis, especially if invading amphibiously or paradropping, is somewhat more flexible than in reality)