Facing same request from expert capacity planner.
It sound reasonable to have immediate outlook of which orders in lower planning grid insist on capacity overload in resource grid by having them on the same bucket column, otherwise different materials with different good receipt processing time will insist on different period in capacity grid with different lag from corresponding quantities in the quantity grid, and the work of manual draft SNP leveling would be a total confusion, made by incremental trials. Incremental modification of quantities bring to fixing of them, so to restart from initial situation planner have to remember modifications made, un fix orders, rechange quantities ... think someone could work like that, really?
Solution found: eliminate good receipt processing time from APO SNP and transfer it in the "safety days supply" field thanks to cif exit on material master --> product master and cif exit on production orders, for the latter to reset GR processing time- Also implemented badi to let also PPDS PPM have a bucket consumption and have a complete view of resources load on SNP side including production order otherwise not loading resource but only visible in 9AFPROD key figure in quantity view.
On the execution system ECC side the good receipt processing time is kept to give correct atp check eg on sales orders.
So product master, SNP planned orders and production orders on APO side have no good receipt processing time, but correct position in time of start=end planned order dates is granted by safety days supply.
You must also then switch off date retransfer from APO to ECC on SAPAPO/CP3 (no retransfer for publication type 31 inhouse production.
Appliable in my opinion if you can use weekly buckets in SNP, fixed duration of one day in PPM/PDS in SNP (processing time of operations of orders rarely Greater than 1 day), accept to have light differences on start and end time on production orders between the two systems (we're not using PPDS) ... so implement also badi on delta report to avoid unuseful errors for such light time differences. No GATP based on SNP planned order in place.
APO leading planning system, also for capacity leveling, so work also for rough cut capacity planning SHOULD be agile having quantities and capacity consumption on the SAME COLUMN!
Total manday effort for all above: 3 days, a reasonable effort, isn't is?