If you don't want to resort to advanced xml, convert your dashboard to a form and add the input type of time. Below is a simple example.
<form>
<label>My Dashboard as a form</label>
<fieldset autoRun="true" >
<input type="time" />
</fieldset>
<row>
<single>
<searchTemplate>mysearch | stats count | rangemap field=count low=0-0 elevated=1-10 default=severe</searchTemplate>
<title>Responses outside SLA</title>
<option name="classField">range</option>
</single>
</row>
<row>
<chart>
<searchName>MySavedSearch</searchName>
<title>My Saved Search</title>
<option name="charting.chart">line</option>
<option name="charting.legend.placement">bottom</option>
</chart>
</row>
<form>
... View more