For CONUS (contiguous US) travel, lodging is reimbursed by the actual amount spent. For OCONUS (Outside of contiguous US) travel, lodging is reimbursed by per diem in addition to meals and incidentals.
The Overnight checkboxes are applicable to OCONUS travel only, for use when traveler is not being reimbursed for lodging by per diem. Select the Overnight checkbox to exclude a day's lodging per diem from the reimbursement request.