The ConvertExternalUserOnStartDateJob transforms the onboardees to employees despite the start date still being in the future.
SAP SuccessFactors Onboarding
The ConvertExternalUserOnStartDateJob will honor the Effective Start Date equal to Job Execution Date only when at least one record of EmpJobInfo entity has the Timezone field populated. Timezone information must be present in emp_job_info_t table. The issue will occur if this timezone information is not configured.
Please refer this guide link for conversion job configuration: https://help.sap.com/viewer/c94ed5fcb5fe4e0281f396556743812c/2105/en-US/b047d17f35a34ec9bd779bd803674de6.html?q=convert%20external%20to%20internal
To resolve the issue for the newly created candidates to be converted only on the start date with the ConvertExternalUserOnStartDateJob run we can create an onChange rule which will populate the value of timezone. Please refer to https://launchpad.support.sap.com/#/notes/2090302 which details the configuration of Timezone.
ConvertExternalUserOnStartDateJob, timezone, future start date , KBA , LOD-SF-OBX-JOB , Conversion External User to Internal User , Bug Filed