This is possible. Let's see how this set goes and if needed then i'll add it in next set.
If i made it so nobody knew who you were declaring against then it would defeat the purpose of the time frame. The whole reason for this is mainly to give nations a little bit of a notice to prepare..
Unless you mean just make it that way in the Global News but still make it so the nation you prepare against knows???? I guess that would be ok..