The blog title and tagline are in #header, and it has 105px of left padding. You need to reduce that as required to get them over to where you want them.
Since I don't know where you want the date in relation to the post title and other meta data, I've just arbitrarily placed it below everything using position: relative; and left and top declarations.
By using position: relative, it will always position the date relative to where it was originally so it will be positioned consistently from post to post.
If you want the date under the post title, then you will need to use position relative and top declarations for the other elements to move them down.