In the blink of an eye
Definition 1 of 1
Pro Tip 1/3Visual Imagery
The phrase creates a mental picture of something happening as fast as an eye blinking. 
He was here, and then in the blink of an eye, he was gone.
Pro Tip 2/3Figurative Use
It's often used metaphorically to express a very brief period of time. 
The seasons change in the blink of an eye.
Pro Tip 3/3Usually Sudden
It implies that the change or event was unexpected or unanticipated. 
The peaceful protest turned violent in the blink of an eye.