I moved this to Bugs as this actually, already happens IF the author of the item has permission to create item without approval, but not if the author does not.
If the Author does not have permission to create items without approval, when clicking on the [Publish now] button (or using the automated scheduling), the item is sent to the approval queue (as is all XF content when the user does not have permission to create content without approval).
I've marked this as "Partially Fixed" as I've made a small minor adjustment to the onPublishDraft() function in the PublishDraft Service, so that the 3 dates applicable to an associated thread get updated regardless of the item state, so even if the item itself is sent to the queue, the associated thread dates get changed to TIME NOW, just like the Item Publish date gets changed to TIME NOW.
The reason for the "Partially Fixed" is that there seems to be some expectations of the Approval Queue changing dates for content and this simply does not happen. None of the Approval Queue handlers for content such as threads change the post_date of a given piece of content that sits in the approval queue. The only thing that the ApprovalQueue handlers do is change the STATE (from moderated to visible or deleted).
So please keep in mind, if the draft or awaiting item that is being requested to be published is sent to the approval queue to be approved, approving the Item will NOT change the Publish date of the Item to the date/time that you approve it in the approval queue, nor will it change the Thread Date and First Post date (that is not something that the approval queue handles). Just like if a newly created Thread goes into the moderation queue on Monday and you approve it on Friday, the Thread Date and First Post date do not change to TIME NOW on Friday when you approved the Thread, the only thing the Approval Service does is change the STATE of the content, so that "new thread" is a week old because it sat in the queue for a week.