How long can the brain survive during ongoing cardiac arrest?
From Boron and Boulpaep textbook of Medical Physiology, second edition, p.289:


  Because of falling ATP levels in the brain, consciousness is lost within 10 seconds of a blockade in cerebral blood flow. Irreversible nerve cell injury can occur after only 5 minutes of interrupted blood flow.


If conscious is lost within 10 seconds of blockade in cerebral blood flow, I guess a person will not be conscious to do any action in only 10 seconds!

Brain ischemia is divided into 


Focal ischemia which signifies stroke. 
Global ischemia which occurs in cardiac arrest. 


Permanent neural injury means that once perfusion is restored, the symptoms don't relieve as the part of brain which caused those symptoms becomes dead irreversibly. 

For a list of symptoms check this page.