Blackout Periods

so i have declared war on someone and went to set my blackout periods and i got this message "Sorry. You cannot change your Blackout Periods when you are in war with another President.".... my question is why? i thought i would declare war and then me and him would go set the times when we didnt want to fight eachother but apparently thats not how it works for some reason?

I'm afraid you can only set your blackout periods if you're not in war.

if you can change them in war, your enemy will never be able to attack as you will change them at will.

also you enemy will do the same and you will probably ask us to remove the blackout periods as you are unable to attack.