IF I am correct, the down times shown are the potential length of time a strat target can remain down AFTER the City Strat, or in the new update, the Industrial Center, is taken below 50%. So, hitting outlying Troop, Ordnance, Fuel, Radar, AAA Factories while the Industrial Center is still above 50% does not affect the down times of the other factories. The Industrial Center supplies all of the other strat factories.
Think of the Industrial Center as being the narrow end of a funnel. If the end of the funnel is unobstructed, material can flow through it easily. However, if you reduce the size of the end of the funnel by crushing it, say 50%, then the amount of material flowing through the end is reduced, and the effect in the game is longer down times for the factories it supports. If you crush the end of the funnel closed 100%, then nothing can flow through it, and the down times for the outlying factories can be quite substantial.
The new twist is, and again, this is IF I am correct, the first time you reduce the Industrial Center to rubble it moves to the rear echelon, and THIS move signals that the Industrial Center is operating at 50% capacity. The outlying strats are not receiving at maximum capacity, so hitting them when they're in the rear will give a bit of down time. BUT! You still need to hit the Industrial Center and take it down below 50% again, while it is in the rear echelon, to get more down time on the other factories. Needless to say, if you completely destroy the Industrial Center while it is in the rear, you will maximize the down times on the other factories when you hit them.
Another variable that pops up is the ability to resupply the Industrial Center/City Strat. Notice the asterisk on the chart by the City Strat...that means it can be resupplied.
