I tried your example. Had to make some assumptions due to different data. So I set span=1h and left out the Target-field (including the overlay).
Problem was then, that I got no data at all due to the _time-fieldformat, which I set to some date/time-string. During drill down I got no data, but - I also got no "invalid earliest_time" error.
You may have a look in the address field of your browser after doing the drilldown. My address contained:
earliest=1529996400.000&
latest=1529996400.001&
which of course are valid times. What's in your address?
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