wrong time display on logon screen

Hi all,

when, let us say at 9:00, i switch on my macintosh, i will have e small time display at the upper right corner at the logon screen. But it doesnt display 9:00, it says 10:00.

Then i logon to my user account. This tells me the correct time 9:00.

Then i logoff and will have the logon screen again. Funnily it now shows the correct time.

What can i do to have shown the correct time on the logon screen immediately after switching the system on?

Mac Pro 5.1 / 2010, Yosemite, Time zone Germany / Berlin.

greetings from germany

Chris