int t = 2000; // Impulsdauer
int T = 2000; // Periodendauer
One letter global variable names are a bad idea. Names that differ only in case are an even worse idea.
Alarm.alarmRepeat(9,0,0,AuslaufAuf); // Auslauf auf um 10:00 Uhr
Alarm.alarmRepeat(22,0,0,AuslaufZu); // Auslauf zu um 21:30 Uhr
If you are going to have useless comments, you must make them agree with the code.
You are setting these alarms before defining the time. It is not clear from the code whether this will work.
You are calling delay(). The documentation clearly says that you must use Alarm.delay() instead.