I've done mine at various times when the light came on, and based on my experience, I would gauge that there is about 7500 wear miles of material left over before your pads wear to the point of scoring the rotors.
I believe MB likes to err on the safe side.
Don't know what model you own, but vehicle weight and driver input are varying factors...but I believe you can probably go a month or two safely before you really need to give the brakes a look...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car