Please refer above subject and would like to do following. External Processing Time I have set in using OPPQ. My client want this time set differently for different Vendor. Is there any userexit or customization settings? 

For MRP to take lead time by supplier, you need to have 3 settings: 

1) The config in OPPQ - External procurement at plant level (or OPPR at MRP grp - Scheduling/doc. type) should have the check box marked to read SchedAgreem/Inforecord leadtime (T399D-GTERM) 

2) You should have a contract/schedule agreement, or a purchase info record maintained for that plant-material-vendor combination 

3) You should maintain source list (ME01) for the contract/schedule agreement, or info record. This changes the default behavior of MRP to use leadtime by supplier, rather than material master leadtime. When both contract and info record exist, the contract will take precedence. 

Please watchout for the case if you're already using contracts/info records in procurement, but not using them for planning. In this case your leadtime data in these documents may be incorrect, or may be left blank - this will be interpreted as zero if you make this change implementation, as mentioned in the steps above. 

Related Links:
Understanding the MRP Rescheduling date
Rescheduling date does not take into account the GR Processing Time

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