Since version 1.9.3, schedules stored in the database app_working_hours are no longer as "XX: XX" but "XX XX h min"
This first case the previous settings.
I also noticed a second bug. Even erasing the lines in the database (trunc) app_wokring_hours, saved schedules are not saved.
I think your problem is in the value of the dropdown that is sanitized and currently Fr WordPress version the value is displayed eg "9 h 30 min"
I had to put a backup of version 1.9.1
Be careful, a minor release should not break like this WebSite