[DOCS] Changes seconds to milliseconds since the Epoch in AD docs. (#53797)

docs/reference/ml/anomaly-detection/apis/flush-job.asciidoc

@@ -98,7 +98,7 @@ on January 1, 2018:
 --------------------------------------------------
 POST _ml/anomaly_detectors/total-requests/_flush
 {
-  "advance_time": "1514804400"
+  "advance_time": "1514804400000"
 }
 --------------------------------------------------
 // TEST[skip:setup:server_metrics_openjob]

docs/reference/ml/anomaly-detection/apis/start-datafeed.asciidoc

@@ -49,7 +49,7 @@ following formats: +
 
 - ISO 8601 format with milliseconds, for example `2017-01-22T06:00:00.000Z`
 - ISO 8601 format without milliseconds, for example `2017-01-22T06:00:00+00:00`
-- Seconds from the Epoch, for example `1390370400`
+- Milliseconds from the Epoch, for example `1485061200000`
 
 Date-time arguments using either of the ISO 8601 formats must have a time zone
 designator, where Z is accepted as an abbreviation for UTC time.