I believe that the
timechart command will remove all unnecessary information.
What you could do is to ensure that your question before the
timechart runs as efficiently as possible, e.g. specifying the correct index and sourcetype, search only for the time range you're interested in. You could even instruct Splunk to not extract any fields at all (
KV_MODE = none in props.conf), and only extract what you need with (an efficient)