What days can you occupy enemy tiles in doomsday events is it limited to week end or all days?

Any day during the doomsday you can take back enemy tiles in your state or travel to an enemy state and take tiles there. You must already have tiles to link from though in the other state (or in your own). If you don;t have tile in the enemy state then you have to wait for a war in the enemy state where you can go and place a rally point to start taking tiles from.