Unable to answer "What are the opening hours here?" for https://osm.org/node/270798652 via StreetComplete 53.3:

The tee house seems to be a customers-only thing for yoga students. None of the postbox refer to it.

Attached photo(s):
https://westnordost.de/p/171294.jpg
https://westnordost.de/p/171295.jpg