My problem is, that my system takes 8 seconds to start the programm after I push the Reset button on my Leonardo. During that period the L-LED is pulsating.
What could be the problem?
That's the firmware waiting for a programming connection. If you want alternate behavior them burn SparkFun's ATmega32U4 firmware to it. One press of Reset will reset the device, and two presses will put it into programming mode.