The time window where you are communicable, mobile and without identifiable pustuals is anywhere from 12-48 hours out of the 17 days. Prior to the on-set of the pox, you are racked with debilitating pain making it impossible for you to function well enough to make a flight.
The time when you start having breath can kill without your being detectable or flat on your back is unpredictable as to both when it starts in that 17 day window and what its length is.