The ViewTemplate piece you want to change is the *subtitle*, defined here: $:/core/ui/ViewTemplate/subtitle
\whitespace trim
<$reveal type="nomatch" stateTitle=<<folded-state>> text="hide" tag="div" retain="yes" animate="yes">
<div class="tc-subtitle">
<$link to={{!!modifier}} />
<$view field="modified" format="date" template={{$:/language/Tiddler/DateFormat}}/>
</div>
</$reveal>
As you can see, it has a $view widget that shows the "modified" field. To add the "created" field, you can
duplicate the existing $view widget and change the field name to "created". You'll probably also want
to add some spacing, punctuation or other static text notation to differentiate it from the "modified" date.
Something like this:
\whitespace trim
<$reveal type="nomatch" stateTitle=<<folded-state>> text="hide" tag="div" retain="yes" animate="yes">
<div class="tc-subtitle">
<$link to={{!!modifier}} />
<$view field="modified" format="date" template={{$:/language/Tiddler/DateFormat}}/>
(created: <$view field="created" format="date" template={{$:/language/Tiddler/DateFormat}}/>)
</div>
</$reveal>
-e