thank you for your answer.
Now I am puzzled.
This "starttime" and "endtime" colored me for all day events the whole dayView. As I do not want this, I made all-day-events "taking place" every day at the same time. This means, if I insert e.g. a birthday, I insert it between 10:00 and 11:00 to have a nice overview every day of what the day will bring.
Back to the problem: I though "endtime" would be 11:00?
In other words: Please explain which parameter to use best for "endtime" of an event versus "endtime" of its alert.