Thanks for the reply.
WU is the trigger.
But now I think there is a misinterpretation of the creator of that applet I did find with the 15 minutes BEFORE sunset.
The original text of the the trigger from WU is "This trigger within 15 minutes of the sunset on your location". So it can be ON sunset or 15 minutes later.
Meanwhile I did find another applet from creator derickpotgieter,
I didnt test that one yet, but I assume he did made the same misinterpretation of the trigger.
In summary, there is obviously no solution to fulfill my wish ;-(