You need to add a token to your input and apply it to the earliest Time latest Time elements for each panel. For example:
<form>
<input type="time" token="timefield1">
<label>Range</label>
<default>
<earliestTime>-30d@d</earliestTime>
<latestTime>now</latestTime>
</default>
</input>
<row>
<panel>
<chart>
<title>CPU Usage</title>
<searchString>index=os sourcetype=performance | timechart avg(CPU) by host</searchString>
<earliestTime>$timefield1.earliest$</earliestTime>
<latestTime>$timefield1.latest$</latestTime>
</chart>
</panel>
</row>
</form>
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