Scheduled posts are published with the modified_date of when you wrote the post and the post_date of when it was published. For a non-scheduled post the modified_date and post_date are the same when the post is published.
Although I use Jetpack on many sites, to be quite honest it still leaves something to be desired in some areas. Fortunately the Jetpack developers are very responsive and make great efforts to improve the plugin with every release. The latest improvement (at least in the current development version) is the ability to add a … ∞
Just a quick note, this site’s theme is now a Child-Theme of Opus Primus. Although there may be a few hiccups along the way, we have decided to add this site to the WordPress Opus Primus Test Venues. Please feel free to report any bugs or peculiarities … or better yet, what you like about … ∞