private com.google.protobuf.SingleFieldBuilderV3<
            com.google.protobuf.Duration,
            com.google.protobuf.Duration.Builder,
            com.google.protobuf.DurationOrBuilder>
        getStartTimeFieldBuilder() {
      if (startTimeBuilder_ == null) {
        startTimeBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.protobuf.Duration,
                com.google.protobuf.Duration.Builder,
                com.google.protobuf.DurationOrBuilder>(
                getStartTime(), getParentForChildren(), isClean());
        startTime_ = null;
      }
      return startTimeBuilder_;
    }
<pre>
Time offset relative to the beginning of the audio,
and corresponding to the start of the spoken word.
This field is only set if `enable_word_time_offsets=true` and only
in the top hypothesis.
This is an experimental feature and the accuracy of the time offset can
vary.
</pre>

<code>.google.protobuf.Duration start_time = 1;</code>
java-speech/proto-google-cloud-speech-v1p1beta1/src/main/java/com/google/cloud/speech/v1p1beta1/WordInfo.java