How do I perform partial deliveries against single order

I have 1 item single sales order with 50 quantities for single customer . I need to do split deliveries of the 50 quantities into 4 customer sites. The known delivery date is for the 1st 15 quantities to be delivered to the first site. the delivery dates for the outstanding 35 quantities on other sites are not known but can be any day after the first delivery. How do I set this up on SAP.