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What is Hyperacute rejection occurs within: and explain in detail?
Ref. Robbins Pathology. 9th edition. Page. 233
 
Hyperacute Rejection

This form of rejection occurs within minutes or hours after transplantation.
A hyperacutely rejecting kidney rapidly becomes cyanotic, mottled, and flaccid, and may excrete a mere few drops of bloody urine.
Immunoglobulin and complement are deposited in the vessel wall, causing endothelial injury and fibrin-platelet thrombi
Glomeruli undergo thrombotic occlusion of the capillaries, and fibrinoid necrosis occurs in arterial walls.
The kidney cortex then under- goes outright necrosis (infarction), and such nonfunctioning kidneys have to be removed.