I often see one of the IMUs at 2 to 4 miles off, but seldom will all 3 be that far off.
Generally, individual IMU drift is 0.0 to 0.4 NM/hour on block-in, which would be as much as 4.4 NM on an 11-hour flight. Usually, at least 2 of them are 0.2 NM/hr or less.