I have some issues with my charts which are empty at the beginning and need about half a day to show anything. Looking into the request logs I discovered that the time is of by 12h compared to the openhab.log file.
Date has the correct time and date in the mysql data base. I suspect that the GET method is querying the wrong time and so the charts are empty at first.
[20/Sep/2015:10:44:45 +0000] "GET /chart?items=HeatPump&period=h HTTP/1.1" 200 6753
22:58:00.531 [DEBUG] [.myopenhab.internal.MyOHClient:150 ] - Transport.EVENT_REQUEST_HEADERS
Date and time are correct on my pi
$ date Sun Sep 20 23:03:10 NZST 2015