Hello
As already mentioned here, using MRP to create the planned orders is the best option. The problem here is that, both the planned order dependent requirements and the production order reservations are relevant for MRP, so MRP would create a planned order for this material even before the order conversion.
I can think of some alternatives for this issue:
1 - Direct the MRP dependent requirements for a storage location excluded from MRP. You can find the setting to exclude a storage location from MRP on the tab MRP4 of the material master (if using the storage location as a selection criteria).
2 - Use BAdI MD_CHANGE_MRP_DATA to make dependent requirements not relevant to MRP. See an example of this BAdI on the blog Making an element not relevant to MRP or MD04 using BAdI MD_CHANGE_MRP_DATA.
If you don't want to use MRP to generate those planned orders, you can use BAPI_PLANNEDORDER_CREATE to generate those orders. Here, you can create your own report to run periodically and generate those orders or trigger the BAPI directly from the production order using a BAdI or exit. See the blog BAdIs and Exits for production and process orders | SCN for a list of those BAdIs and exits.
BR
Caetano