Bulk delete by powershell

Got a training environment where students creates various pages etc. in the top-level site and the subsites, in order to become real editors in our production environment. (publishing site)

I would like to "reset" the training environment after a class session and delete all the pages, documents, images etc. that the student have created/uploaded on that specific day. 

Can someone provide the powershell script syntax (by date - not user) in order to do this?