You used to as long as you were actually resupplying someone while you were still up.
Not as long as I'm playing AH though.
What would the supply trucks have to do with it?
They impact downtime of already destroyed objects - but only when destroyed
You bring in supps - 10 minutes off the object's downtime
Enemy kills a convoy - slaps 7 minutes on top of the object's downtime.
then why does the system say it took 10 minutes off?
Because that's how it works. Every drop of supps reduces downtime of all resupplyiable objcets in range by 10 minutes each.
Supply trucks would only make the object come up even faster if they were running.
Supply convoys are always running (every 10 minutes) and have no actual effect as long as they do. Only when a truck/train/barge is destroyed, it puts some extra downtime on the objects already destroyed at that base.
That being said, judging by the numbers presented I still think it's a bug. One I have never encountered so far.