Заранее спасибо

http://books.google.ee/books?id=uQhZ4yajjOgC&pg=PA327&lpg=PA327&dq=slot+charter&source=bl&ots=gn05J8HyuY&sig=fGiONpHt1JjCvVm6q_MZcipRt4A&hl=es&sa=X&ei=8aO2T8GsG8z34QT_vvjcCQ&redir_esc=y#v=onepage&q=slot charter&f=false

http://www.cargoprime.ru/cargoprime/cpkt/functions/06.php

2. Vehicle Booking Slot

P&G will ensure all hauliers are aware of the destination details, including warehouse opening hours. 3PL will manage unloading slots to ensure demurrage charges are not incurred. 3PL will track arrival time (i.e. when the driver registers with 3PL dispatch office), beginning and end of unloading time for each vehicle as well as departure time (i.e. when all proper documents are returned to the driver) and ensure that correct arrival/departure time are noted in SAP, on each CMR/waybill and on any other transport time-sheets.
Each unloading gate should be equipped by video camera. Video camera records must be kept at 3PL for 3 months at least and must be provided to P&G upon request within 2 business days.

unloading slot = slot for unloading

Словарь:
slot
…4) (amer) размеченное место для парковки автомобиля

Далее по принципу a person (is) booking an apartment in a hotel
читаем словосочетание
[a] vehicle [is] booking [an unloading] slot