Hi Hauke,
Just an idea for another approach. You could consider to enhance your Process Chain with Decision Between Multiple Alternatives. Here you can check on local system time (SYST-TIMLO). If the system time is between 09:00 and 18:00 h, then execute the normal process steps, otherwise end.
This way the Process Chain will run hourly, but only between 09:00 and 18:00 h it will execute the process steps. Outside the time window it will immediately stop processing.
Best regards,
Sander