Unable to answer "What are the opening hours here?" – River Habitat (Real Estate Office) – https://osm.org/node/4226087378 via StreetComplete 57.4:

Location closed? - see photo, looks kind of deserted too
No opening hours sign anyway

Attached photo(s):
https://westnordost.de/p/216443.jpg
https://westnordost.de/p/216444.jpg