Wrist hinge should happen naturally in your golf swing.
If your grip is in a neutral position, your wrists will be able to fully hinge as you swing the club back to the top. There is no exact spot where you are supposed to hinge your wrists. Some players set their wrists very early in the swing, and others create the hinge later in the swing. Most high-handicappers go wrong when they have no wrist hinge and end up hinging their elbows instead to get the club to the top.
