In determining the averages required in Section 11293, the board shall exclude from the California factor car mileage, car days or such other data which occurs while cars are not qualified for revenue service and are in a repair facility in this state requiring and undergoing or awaiting remodeling, overhaul, renovation, conversion or repair which necessitates total labor in excess of 10 man-hours.

Car days excluded pursuant to this section shall not exceed 90 days per car unless the claimant provides substantiation of the necessity for the additional days in such form as prescribed by the board.