private Timestamp parseTimeStamp(Tree offsetNode) {
    if (offsetNode == null) {
      return new Timestamp();
    }
    List<String> s = new ArrayList<>();
    s.add(TimestampParser.ISO_8601_FORMAT_STR);
    s.add(TimestampParser.RFC_1123_FORMAT_STR);
    s.add("HH:mm:ss");
    s.add("H:mm:ss");
    s.add("HH:mm");

    TimestampParser p = new TimestampParser(s);
    return p.parseTimestamp(unescapeSQLString(offsetNode.getText()));
  }
Composes an overlay object.

Output is a flattened view of the input objects.
having the value from the first one which has it defined from the overlays.
ql/src/java/org/apache/hadoop/hive/ql/parse/ScheduledQueryAnalyzer.java