Prerequisites 

  We have to setup following either 1 or 2 to achieve this

 By default, Oracle Purchasing Cloud attempts to create Purchase orders from Requisitions immediately upon requisition submission. 

The first step is to defer purchase order Creation until to any weekday say Monday

1)To defer order creation, you need to perform any of the following actions:o defer order creation for imported requisitions or requisitions created using web services, disable the “Create orders immediately after requisition import” option in the Configure Requisitioning Business Function.

2)To defer order creation for requisitions created in the web interface, enable the Consolidate Requisitions into Fewer Orders feature.

After that you have to define schedule group

And we have to attach schedule group to BPA (Blanket Purchase Agreement )

After that you have to schedule the "Generate Orders'

For more information you can watch the video