For a deeper look into our World Check One API, look into:
You can look at the attribute "creationDate" of the JSON response of the API call- "SEQ-screen-sync-individual: Perform Synchronous Screening: Individual" or "SEQ-case-investigate-results: Get screening results" of every match of the result set to find out the when a match was generated in a case. Generally, the value of the attribute "creationDate" is same for all the matches but if you rescreen your case or if OGS is enabled in your case, then you may find different dates for different matches on the same case. The reason being the OGS or rescreening may generate matches at a later date and that is recorded by the attribute "creationDate".
Also, you can look at the attribute of "creationDate" of the API call "SEQ-case-investigate-case-details: Fetch full case details" to know when the case was first screened. But this will not reveal when the new matches were generated to OGS or rescreening on an old case.