@Anonymous This sounds very strange. If you are using your carrier's voicemail system, the voicemail timestamps would be something that they would add. So it implies that the carrier's time frame is off. Which carrier are you using? Are you using multiple SIMs?
BTW, Germany is always behind the US. When it is 10 am in New York it is 4 pm in Germany.
@Anonymous Sorry, I guess I should have said their time is "later" than the US, rather than "behind". If you received a call at 10 am New York but the VM system is set to Germany time, the timestamp would be 4 pm.