You need to set up the system to manage the work hours template for all...

Go to the resource and select the Working hours tab.

Set the resources in the correct time zone.

Create a work hours template based on the region.

Create new working hours, then select Repeat as "custom", with "Monday to Friday' and the hours set as "8:00 am to 5:00 pm'

Select the resource, set the calendar, and apply the working hours template.