Normally, the planned order determined the date from Material Master.  The Planned Order created by the MRP reads the production capacity requirement from Material Master. (MM03 – Work Scheduling – Lot size dependent in-house production time).  When you convert the planned order to a production order, SAP determined the date from Routing.

User Requirements:-  Planned and Production Order should read the requirement from routing.

Solutions:-
Run MRP Scheduling -> 2 – Lead time scheduling and capacity planning

Transaction OPA9 (Sel. Profile - SAPA010) - Change configuration for Capacity Planning to read Production Order.  Untick the Planned orders under the Order categories.

SAP PP Reference Books:
SAP Production Planning , Configuration, Interview Questions and Certification, Books

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