[days[-14]]
[!days:created[-800]]
The filter can be used to highlight new items in a list. For example:
<ul>
<$list filter="[tag[ReleaseNotes]!<currentTiddler>!sort[modified]]">
<li>
<$link><$view field="title"/></$link>
<$list filter="[<currentTiddler>days[-180]]"> @@color:red;^^new^^@@</$list>
<$list filter="[<currentTiddler>days[-500]!days[-180]]"> @@color:black;^^recent^^@@</$list>
</li>
</$list>
</ul>
That renders as: