The Triumph of the Lamb Vol 3
It should not strike the Christian as strange that right now there is a great and terrible warfare going on in the spiritual realms. It is an invisible war that is unseen to us. But that does not mean the effects of that war are unfelt or not being played out on our soil.
I think it really is O.K. not to try to answer the question of when this war arose. The point of the vision is not to identify the point in time when this happened, the point is to identify the great spiritual conflict between Satan and his angels, that is the demons and Michael who has a great military made up of angels.