I wouldn't recommend that....that provides the datetime the job completed, not the date of the extract. It's conceivable (OK, odds are low, but it's conceivable) that rows could have been added between the time of the extract and the time when the job posts as complete to the windows event log.

The best practice is, back in the query, to do this in a txaction and then post the date to a log table, and use THAT date as the basis for subsequent extracts.