When using the Skillsoft Connector, the course duration is being populated into the "Credit Hours" field, but you would like to use the "Length" field instead.
Skillsoft Connector will put the "duration" value in the "Credit Hours" fields because this is the default connector mapping and this value must not be changed.
LMS is working as designed and a change in this functionality would require an Enhancement Request to be submitted at https://influence.sap.com/successfactors
Default Column Mappings for Skillsoft Connector
How to submit enhancement requests for SAP SuccessFactors products
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