Each member has their own available hours that determine their start times. To update them you'll want to edit your staff members. Here is a step-by-step guide to updating the frequency of the times.
Choose "Members & Availability" from the left navigation
Select the member whose schedule you want to update
Click the "Available Hours & Meeting Types" panel
Click on a range of time from your schedule
Change the frequency to the desired period and click "Save Changes"
There is a second Save Changes button on the right side of your member page. Click this button to complete the process.