Hi Peter,
The requested delivery date is the date that the customer is requesting the material arrive at their site. Therefore, the logical calendar to check this against is the unloading point calendar of the customer. Please maintain an unloading point and assign a calendar for the customer in transaction VD02.
When you do this, the system will issue a warning of you enter a non-working day. There is not possibility to change this to an error in the standard system. The system assumes that the user knows what they are doing and takes priority over the warning message. However, the warning message does inform the user of the next working day.
I remember replying to a similar thread about this before. You can find it here: