I can envision that timestamp being transcluded in "Tool" right under the wiki version number or in Control Panel along with number of tiddler & overwritten shadows. I often use a similiar idea with wiki's I customize for ppl-- its default startup tiddler will have a last updated text line using last modified non-system tiddler.
The bit of code I posted above I took even further-- made it into a wiki monitor (like FF web tools' log fundtion), it can show:
* what the wiki does-- a partial behind the scenes view-- when you're opening & closing tiddlers, clicking tabs
* or display temp and state tiddler updating-- to check if your buttons, sets are doing what you hope they should be doing
Using esoteric wiki wizardry formulas (ie: this and that and some of that = looks like it worked)-- the last wiki activity code and html code block in lists and my fields diaplay code into that below
__LATEST WIKI ACTIVITY__: <$list filter="[all[tiddlers]!sort[modified]limit[10]]">
<$view field="title"/> - <$view field="modified" format="date" template="DD mmm YYYY 0hh:0mm:0ss"/><br/>
</$list>
__LAST 10 TEMP STATE ACTIONS__:<br/>
tiddler title - modified date/time<br/>
``text field contents``<br/>
``custom fields`` content (if any)<hr/>
<$list filter="[prefix[$:/temp]] [prefix[$:/state]] +[!sort[modified]limit[10]]">
<$view field="title"/> - <$view field="modified" format="date" template="DD mmm YYYY 0hh:0mm:0ss"/><br/>
<pre><$view field="text"/></pre>
<$list filter="[all[current]fields[]sort[title]] -[all[shadows]removeprefix[$:/language/Docs/Fields/]] +[append[list]]" variable="listItem">
<span class="rspannbrk"><span class="ragsspannumb"><$text text=<<listItem>>/></span> <$view field=<<listItem>>/></span>
</$list>
<hr style="border:dotted 3px;"/>
</$list>