How to set BLDAT on a different value than BUDAT with BAPI_PRODORDCONF_CREATE_TT?

Im using BAPI_PRODORDCONF_CREATE_TT to create a Prod-Order. I set postg_date in the Structure for the Timetickets to our budat, but that also changes everytime the bldat in the mkpf.

How to avoid that? we want budat to a custom date, but bldat the current day. Debugging, googling and looking through the structures didnt help at all