The Post Reversal Script (PRS) is a drop-in hack for reversing the chronological order of Blogger blog posts from the newest-to-oldest default arrangement to an oldest-to-newest arrangement.
To use the script, edit your blog template, paste the script in just before the </body> tag, save the template, and view or reload the blog. The posts both on different days and within each day should then appear in oldest-to-newest order.