Charges may be assessed to cover the cost of travel time incurred in connection with the performance of any inspection service, including appeal inspections, as described in § 52.42. This includes time spent waiting for transportation as well as time spent traveling, but not to exceed eight hours of travel time for any one person for any one day: And provided further, that if travel is by common carrier, no hourly charge may be made for travel time outside the employee's official work hours.