Seven Days — Ben Hale

Forced to ally, the world has gathered against the endless night. Numbering over a million souls, they are the survivors of nations. They have armed themselves with weapons and magic, and defend the strongest fortress every built. Led by a supreme strategic mind, the races have organized into battalions, designed unique tactics, and fortified their position beyond any conceivable need. But now their foe is at their gates, and to a man they cling to the same hope, to survive until Elseerian can defeat the source.

The best they can last is Seven Days . . .