I could find out the code for displaying a widget (say image) only on a particular label page but I am not sure how to get it on a particular month. If you provide me an exact explanation of how you want it by month I can try exploring it. Here is the code for label pages. The "if" construct is in bold. Remove the [ ] but not the quotation marks while using it:

First Add page element of text or HTML. Name it (i.e title) anything, for example milan.

go to Layout >> Edit HTML.

Tick Expand Widget Templates.

Find newly added widget i.e serch for milan

<b:widget id='Image1' locked='false' title='milan' type='Image'>
<b:includable id='main'>
<b:if cond='"[your label URL in these quotation marks]" == data:blog.url'>
<b:if cond='data:title != ""'>
<h2><data:title/></h2>
</b:if>
<div class='widget-content'>
<img expr:alt='data:title' expr:height='data:height' expr:id='data:widget.instanceId + "_img"' expr:src='data:sourceUrl' expr:width='data:width'/>
<br/>
<b:if cond='data:caption != ""'>
<span class='caption'><data:caption/></span>
</b:if>
</div>
</b:if>
</b:includable>
</b:widget>

Add red code line. Don't forget to place url of the lable.

Save template. You are done. Now the widget can be seen on lable only.