TileNotification.ExpirationTime | expirationTime property

var expirationTime = tileNotification.expirationTime;
tileNotification.expirationTime = expirationTime;

function tileNotificationExpiration() {
    var Notifications = Windows.UI.Notifications;
    var tileXml = Notifications.TileUpdateManager.getTemplateContent(Notifications.TileTemplateType.tileWideText04);

    var currentTime = new Date();
    var seconds = 30;

    var tileTextAttributes = tileXml.getElementsByTagName("text");
    tileTextAttributes[0].appendChild(tileXml.createTextNode("This notification will expire at " + new Date(currentTime.getTime() + seconds * 1000)));

    var tileNotification = new Notifications.TileNotification(tileXml);

    // Set the expiration time on the notification
    var expiryTime = new Date(currentTime.getTime() + seconds * 1000);

    tileNotification.expirationTime = expiryTime;
    Notifications.TileUpdateManager.createTileUpdaterForApplication().update(tileNotification);
}