. . . . "(b) The schedule of charges in paragraph (a) (1) and (a)(2) contemplates that those charges are calculated per man/per hour, or per man/per day, provided that where attendance of customs officers as paragraph (a)(1) is off Tutuila Island, the cost of travel, per diem, or other costs, including overtime, will be charged and collected from whomsoever requires such off-island attendance of customs of" .