To be competitive it is essential for all players to operate on the same time scale. The fundamental time unit of the game is the "turn" and there should be no way that the timing of a character's activity within that unit is significant. That is to say "real time" factors should not influence the gameplay.
One obvious way they do is the obsession for early military orders. There can be no doubt orders issued early in the turn will be received by more characters than late ones and therefore overall response rate will probably be influenced.
The simple answer is for all actions, including messaging, to be resolved at the start of the next turn.
