It is totally possible to postpone your storage service. The conditions of postponement depend on the type of service and the date on which you make your request.
For paid collection and redelivery services, you will have to make your request for postponement 3 days before the date initially planned. In case you make your request 72 hours before or less, you will have to pay 50% of the fees.
For free deliveries, the 3-day deadline remains the same. But in case you make your request 72 hours before or less, you will lose your monthly free delivery advantage for the current month. You will have to wait for the next month to have your stored items delivered, or go through a paid redelivery.