public Builder setStartTime(com.google.protobuf.Timestamp.Builder builderForValue) {
          if (startTimeBuilder_ == null) {
            startTime_ = builderForValue.build();
          } else {
            startTimeBuilder_.setMessage(builderForValue.build());
          }
          bitField0_ |= 0x00000002;
          onChanged();
          return this;
        }
<pre>
Optional. The starting timestamp for messages to import.
</pre>

<code>
.google.protobuf.Timestamp start_time = 2 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/SlackSource.java