My guess would be from Germany and since they don't have a lot of experience in this, will micromanage this to the nth degree to minimize any liability and of course to ensure your safety. Now if you told me this is simply plug and play and any mechanic could swap out the motor, i.e. screw on and attach the leads, that might be a different story.
If I were either one of you, I would be all over them to ensure they did it correctly and once two weeks went by, do my best Larry David impression and demand a refund of new car, of which they have plenty lying around unsold. You are the ones being inconvenienced as they figure this out.
Jeff in NYC
MB '17 B250e; MB '06 E500W; MB '81 380SL