The Posting History will show you the date and time an advert was posted to each board and the date of expiry or deletion. It will also show every instance that the job has been resent without changes.
The Posting History can be viewed in two ways. You can click the plus sign on the right hand side of a job title in Manage Adverts (this will show a recent history) or you can view the information in the Advert Details page (for a full history).