Delivery before the schedule line date in scheduling agreement.

Hi All,

I have a situation where in I am using JIT delivery schedule for processing the delivery requirement from customer. In this, lets say, I have a schedule as 08/05/2009 for material A to deliver 1000 qty and the material is made available to me after production as of 07/05/2009 and I want to despatch the material on 7th only and not on 8th. The system does not allow me to do this.It allows me to make a delivery only on 08/05/2009.

Is there any alternative to this and is this SAP standard behaviour.