After the key will turn in the ignition switch you may still have to wait until the shifter can be moved from PARK. This can take from several minutes to several hours, depending on the ordering method used to obtain the replacement keys. A few weeks ago I had to learn new keys to a 2003 S500. The first key was learned almost immediately. The second key took about three hours before it would turn in the ignition switch, then another hour before the shifter could be moved from PARK. Of course, I'm assuming you bought your key from an MB dealer and not e-bay.