code: protected FlinkKafkaConsumerBase<T> setStartFromTimestamp(long startupOffsetsTimestamp) {
  		checkArgument(startupOffsetsTimestamp >= 0, "The provided value for the startup offsets timestamp is invalid.");
  
  		long currentTimestamp = System.currentTimeMillis();
  		checkArgument(startupOffsetsTimestamp <= currentTimestamp,
  			"Startup time[%s] must be before current time[%s].", startupOffsetsTimestamp, currentTimestamp);
  
  		this.startupMode = StartupMode.TIMESTAMP;
  		this.startupOffsetsTimestamp = startupOffsetsTimestamp;
  		this.specificStartupOffsets = null;
  		return this;
  	}
docs: Version-specific subclasses which can expose the functionality should override and allow public access.