We document how to send push notifications using Mobile Services fairly well.  You can use the wns object and push the notification.  This is documented here:

Get started with push notifications in Mobile Services 

Push notifications to users by using Mobile Services

What is not documented until now is how to expire the notification after a certain time period.  This is actually very easy (especially now that I have documented it)!

What you want to do is to pass this header: X-WNS-TTL and the number of Seconds you wish this notification to live.  Here is an example of how to do this:


   { text1: item.id, text2: item.text },
       headers: { 'X-WNS-TTL': 30 },
       success: function (error, result) {

This example will expire the tile 30 seconds from now.  The key here is that the second object passed now has the headers option specified (https://github.com/tjanczuk/wns).

Here is some further documentation on that header:

Push notification service request and response headers - X-WNS-TTL


Let me know if this helps!