Hello Daniel,
Production order always schedule by routing lead time of operations. I don't think in standard SAP it is possible to schedule production/process order with in-house time from material master.
In-house production time is to determine the planned dates for planned orders in materials planning.
You should make sure that the in-house production time defined on the material master is as close as possible to the times defined on the routing, so that the basic finish date matches the production finish date.
You can get the update In-house production time in material master value from the routing
Transactions CA97 or CA97N can be used to update the in-house production time with the information from the routing.
Best Regards,
R.Brahmankar