hi!
Thanks a lot for your answers! When I asked this question I already had another test running. Before I did that test I had a clean of all O-rings and the housing (all O-Ring positions). When I came back from work yesterday the vacuum was still stable after 9hours. I don't know exactly what it was but there are three possibilities:
- O-rings not clean
- Vacuum ventile not completly closed ( possibly I didn't close it to the end, because I am careful: I have strong hands and after closed there often comes: broken ;-)
- I just gave it a very light vacuum (finished directly after green light). It was warm in the evening when I closed it and ca. 5 degree Celsius colder in the morning. So maybe the pressure-difference was just a little to much (the light was orange NOT red, means a small loss of vacuum was detected, but not a complete loss)
I have no idea what it was, but it is good to know your experiences to avoid any leak of the housing!
As a result I will definitly go down with the housing, but without camera the first time 
Just to make this thread complete and make it even more interesting for others:
How long before a dive do you normally prepare your housing? Nauticam says (for E-M10) at least 30mins. After what time do you "trust" your vacuum detection system?