Ofcourse as fast as light is ! As per the Theory of Relativity the max speed will be that of light & any thing above c ( speed of light) will cause the time to go back.( you will go back to UKG / KG).Nothing meant to wound you personally.
Lightning altitude can be determined calculate the time to hear the sound multiply by velocity of sound.
Discharge happens less than a second you know earth is positive in charge from earth it initiate.