When shooting with Live View and using Speedlite flash, you may hear the shutter sound twice. This is not the camera taking two images, but simply the shutter closing to be able to carry-out flash metering. Because of this, the time between pressing the shutter button and the image being taken will be slightly longer than when shooting without flash. If you need the shortest lag possible between pressing the button and the image being taken, you should turn Live View off and shoot using the viewfinder.
- EOS 7D Mark II