To use a DB result field as the event time, then do this:
| dbxquery connection=your.db.connection query="SELECT createdAt, name FROM some_table" | eval _time=strptime(createdAt, "%Y-%m-%d %H:%M:%S") | timechart span=7d count by name
This assumes date/time fields come back from your DB like 2017-10-16 16:20:00.
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