I would say wait until your letter comes. However, if you have your vehicle at the dealership and the campaign appears on the VMI (history check) we run when you come in, we will have to do it then and there.
If your vehicle makes any of the strange noises/vibrations discussed in many of the previous H/B threads, I would come in right away to have it checked.
You can also always call the MB CAC at 1-800-FOR-MERCedes for some more detailed info, or at least some company jargin. Good luck.
DR.D