Unable to answer "What are the opening hours here?" – Rathaus (City Hall) – https://osm.org/way/173763773 via StreetComplete 59.2:

Rathaus/Stadtverwaltung allgemein:
Mo - Fr 08:15-12:30h,
+ Do 14:30-17:30h

Darin das Bürgerbüro:
Mo 07:30-17:00h
Di 07:30-17:00h
Mi 07:30-13:00h
Do 07:30-18:00h
Fr 07:30-13:00h
Sa (jeden 1. im Monat) 09:00-12:00h

Daneben die Tiefgarage:
Mo - Fr 07:00-20-30h
Sa 08:00-14:00h