At the bottom of most Blogspot posts you will find a link like the following:
Subscribe to: Post Comments (Atom)
When you click on that it will show you a code dump. It is the RSS feed for that particular post, including all the comments.
All you need to then do is look for the comment you're interested in and then go to the first
<published> that you see before it. That will contain both the time and date the comment was posted.
For example, here's a snippet of what it might look like when you click directly on that "Post Comments (Atom)" link:
<title type='text'>have you read Rothbards Ethics of Liber...</title>
<content type='html'><i> [...] </content>
If you open the link in certain browsers, like Firefox, it's much easier to see:
have you read Rothbard's "Ethics of Liber...
Tuesday, 3 June 2014 12:10
have you read Rothbard's "Ethics of Liberty"? [...]