This idea has been launched before, but Bytro was less than enthusiast so it won't happen.
It would make games timezone-specific, and thus harder to fill rounds. Your 12h "daytime" doesn't correspond to someone elses; furthermore, people may not be able to play from work as well so they'll want 4-hour games rather than 12h ones. The diversity of personal day schedules is endless and you can't possibly cater to everyone.
So until then, what you need to learn is, damage control in case of unexpected overnight events:
- NEVER leave your planes patrolling over the battlefield. NEVER! Let them patrol as far back as you can from their current airbase; that should be enough. It will take you less than an hour next morning to get them back in full-fledged action.
- When you're blitzing, let the attack arrows end just BEFORE the last province dot, rather than actually going all the way. If there is a dangerous enemy stack, you have a decent chance he's offline as well and you can sneak back. You CAN continue your blitz overnight when you have scouted well, though of course it is more dangerous.
- When you're attacking, use delay. You can time your armies to start marching an hour or two before you wake up, then start the actual attack over breakfast.
- When you're at peace, don't defend the first province against a possible overnight attacker, but keep your troops 3-4 provinces behind. That's usually enough to survive for a full eight hours even if you ARE attacked at the worst possible moment (just 10 minutes after you doze off).
- When defending, concentrate troops in the evening in bigger stacks. It is simply harder for an enemy to kill many stationary troops in the same place, than mopping up many isolated units. Ground is easier to recover than troops.
There's really no need to lose sleep over the game... after all, it IS "just a game" though I realize that statement can sound ridiculous when you're really hardcore. But in the end, you play it for fun; and even losing a round is better than walking around like a zombie all day because you didn't sleep enough.