public Builder clearStartTime() {
      bitField0_ = (bitField0_ & ~0x00000002);
      startTime_ = null;
      if (startTimeBuilder_ != null) {
        startTimeBuilder_.dispose();
        startTimeBuilder_ = null;
      }
      onChanged();
      return this;
    }
<pre>
Output only. Marks the beginning of execution.
</pre>

<code>.google.protobuf.Timestamp start_time = 2 [(.google.api.field_behavior) = OUTPUT_ONLY];
</code>
java-workflow-executions/proto-google-cloud-workflow-executions-v1beta/src/main/java/com/google/cloud/workflows/executions/v1beta/Execution.java