War table Bug - Timed Missions

You don't need to leave your console on for the timed War Table missions, they go by the system clock, not by how long you've been in-game. Changing your system clock can do weird things to any war table missions you have active in the game, whether you're actively playing it or not.
Some missions are very long (a day, perhaps longer), a good way to check if it's saying longer than it should is to check the mission on the wiki, it should tell you the completion time (though it varies whether agents are taken into account, they don't make all that much difference).