Blogger: Get Url of First Post

The Solution
Edit the blogger's template to include the following javascript code:

<script>
function getFirstPostLink(){
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.src = '/feeds/posts/default?alt=json-in-script&max-results=1&callback=parseRsp';
    document.getElementsByTagName('head')[0].appendChild(script);
}
function parseRsp(root){
    var feed = root.feed;
    var e0 = feed.entry[0];
    var firstPage = e0.link[2].href;
    // use the firstPage lin: window.location.href=firstPage;
}
getFirstPostLink();
</script>

Resources
Advanced Blogger Feeds Settings
Blogger Feed URLs