How can I change working hours?

When I set up all of the services and providers, I set it up to work from 8AM to 10PM. I now want to change it to 8:30AM to 10PM.

I have the settings as 30 minute increments and have changed everything to 8:30AM to 10:30Pm but the calendars aren't updating. They are still showing 8AM. HELP... how do I get it changed without deleting all of our current appointments and starting all over?