title: Different result for [NSDate date] in several devices
body: <p>To start, I have to say that I set autoset in date&amp;time settings and time zone is the same for each device. So I use <code>[NSDate date]</code> to get time stamp in milliseconds, then encode to <code>NSData</code> and send to another device. On receiver data is being decoded and subtract with new <code>[NSDate date]</code>. So that I get total time needed for send and receive message. That I was thought because when sender is iPhone 4 iOS6 and receiver is iPhone 5 iOS7 then receiver have earlier time stamp than sender. I don't know why? Maybe <code>[NSData date]</code> isn't the most reliable class for that kind of operations? I use <code>GCDAsyncUdpSocket</code> for sending/receiving UDP.</p>
  
  <p>Code sender</p>
  
  <pre><code>NSData *data2 = [self createRandomNSData:8192];
  NSMutableData *dataToSend =[NSMutableData data];
  [dataToSend appendBytes:&amp;tag length:sizeof(int)];
  long long currentTimeStamp = (long long)([[NSDate date] timeIntervalSince1970]*1000.0);
  [dataToSend appendBytes:&amp;currentTimeStamp length:sizeof(long long)];
  [dataToSend appendData:data2];
  NSLog(@"%i || %lld || %lu",tag, currentTimeStamp,(unsigned long)[dataToSend length]);
  [_udpSocket sendData:dataToSend toHost:@"230.0.0.1" port:_port withTimeout:-1 tag:tag];
  tag++;
  </code></pre>
  
  <p>Code receiver</p>
  
  <pre><code>char* dataBytes = [data bytes];
  int inTag;
  long long inCurrentTimeStamp;
  [data getBytes:&amp;inTag length:sizeof(int)];
  [data getBytes:&amp;inCurrentTimeStamp range:NSMakeRange(sizeof(int), sizeof(long long))];
  long long currentTimeStamp = (long long)([[NSDate date] timeIntervalSince1970]*1000.0);
  long long timeStampDiff = currentTimeStamp - inCurrentTimeStamp;
  self.delay = timeStampDiff;
  NSLog(@"%i || %lld || %lu",inTag, timeStampDiff,(unsigned long)[data length]);
  </code></pre>