After updatng to ownCloud 9, the settings for time display and start of the week day were gone!
According to ownCloud/Calendar Issue #340, this is intentional:
The settings for 12h/24h and "Start week on" are now linked to the language the user chooses.
For users like me who prefer English UI, but with European calendar settings, there's luckily a workaround:
Switch the language to:
This keeps the UI in English, but sets start of the week to "Monday" and time display to 24 hours. *phew*English (British English)