private com.google.protobuf.SingleFieldBuilderV3<
            com.google.protobuf.Timestamp,
            com.google.protobuf.Timestamp.Builder,
            com.google.protobuf.TimestampOrBuilder>
        getStartTimeFieldBuilder() {
      if (startTimeBuilder_ == null) {
        startTimeBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.protobuf.Timestamp,
                com.google.protobuf.Timestamp.Builder,
                com.google.protobuf.TimestampOrBuilder>(
                getStartTime(), getParentForChildren(), isClean());
        startTime_ = null;
      }
      return startTimeBuilder_;
    }
<pre>
Time when the request was received.
</pre>

<code>.google.protobuf.Timestamp start_time = 1;</code>
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/SynthesizeLongAudioMetadata.java