Post date not honored on front end

[sjohnson32]

I've imported old blog entries into my staging site for use in the InstaBlog plugin.
When I view the entries date in the admin I see the correct post date for each entry. But on the blog page where the entries are displayed, the date of the import is displayed rather than the post date.
The InstaBlog template uses this to display the date:

{{ blog.postDate.format('F d, Y') }}

This may be a question for the InstaBlog forum, but do I need to make a change here to display the correct post date?