Like this:
<form>
<label>Using half of timepicker</label>
<description>Using half of timepicker</description>
<fieldset autoRun="true" submitButton="false">
<input type="time" token="time_tok1" searchWhenChanged="true">
<label>Chart Timespan/Width</label>
<default>Last 24 hours</default>
</input>
</fieldset>
<row>
<chart>
<title>Using earliest only</title>
<searchString>earliest=$time_tok1.earliest$ latest=now() Your Search Here</searchString>
</chart>
</row>
<row>
<chart>
<title>Using latest only</title>
<searchString>earliest=0 latest=$time_tok1.latest$ Your Search Here</searchString>
</chart>
</row>
</form>
Uhh...could you clarify what you want to do a bit more please?