HOW ARCHIVE ONLINE WORKS DURING ETL operation

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HOW ARCHIVE ONLINE WORKS DURING ETL operation

I know Archive Online meant to backup online but how it works in underlying scenario

6th July ETL under process not completed yet 

I started archiving online a database at 8 AM which was under process (ETL jobs were loading data into that)

ETL jobs are completed at 11 AM

Archive operation is completed at 5 PM

How can I validate what data has been archived 

Thanks in anticipation