Set work hours/timezone for Resource Rooms
Set-MailboxCalendarConfiguration -Identity "<room name>" -WorkingHoursStartTime <start time> -WorkingHoursEndTime <end time> -WorkingHoursTimeZone "<timezone>"
Live example:
Set-MailboxCalendarConfiguration -Identity "Conf Room_One" -WorkingHoursStartTime 07:00:00 -WorkingHoursEndTime 20:00:00 -WorkingHoursTimeZone "W. Europe Standard Time"