how soon should brake pads be replaced

depends on how heavy your foot is,on how long they will last! if the front and rear need replaced for your 2017 Mercedes-Benz S63 AMG then $470.00 to $700.00. I don't own a Mercedes,just an ole pick up and got 83,000 miles out of the last set of pads,less than 100 dollars for ceramic pads,including turning the rotors also.you will need to have them inspected to be sure if you need them or not.

How many miles on vehicle?