Hi,
left the sim by closing it on the console (XBOX S), without save it to a .flt-file. Then next morning re-start the XBOX and started the sim, which is resulting in a "quick resume". With a "quick resume" the sim starts inmediately the flight how and where it was, without loading a .flt-file (even without starting the main-screen of the sim, https://support.xbox.com/en-us/help/games-apps/game-setup-and-play/get-back-to-your-game-instantly-with-quick-resume).
The time on the cockpit-clock was the same as when I left (02:20 pm for example). But the ET (elapsed time, third line on the clock) was 1:30 when I left and now 7:50. So it counted the time of me sleeping 😉. I suppose it uses the system-time of the console to calculate the flight-ET.
Sorry, in first post I forgot to mention that I am on XBOX.