I wish to show time from the last blog update in the header of my wordpress blog. It isn't the final update duration of a publish but instead any publish or page (i.e. any last update completed in your blog)

e.g. Format:

Now: Tuesday, March 16, 2010 | Last Update: 6:09 PM ET

Can there be any template tag to do this?

I'm not sure associated with a template tags that may do that, but you have access to the database directly and discover the "latest" publish or page. Try something similar to this (I've no wordpress-installation readily available for test at this time):

<?php $newest = $wpdb->get_row("select post_modified from $wpdb->posts 
where post_type in ('page', 'post') and post_status = 'publish' order by post_modified desc");
 echo mysql2date('m/d/Y',$newest->post_modified);
 ?>

An immediate answer from here