Hi, I had this issue as well - the fix for me was to change the work hours from Outlook on the web, as the Outlook desktop client is currently broken, with the inability to save work hours.
Click the gear wheel, then choose Calendar, work hours and location, and change the start time to 9am (or whatever time you start). When you change this, it will give you the option to save, and then after a few minutes restart outlook desktop and it will work.