Since the inquiry is about tense, it should be pointed out that the construction is generally followed by present perfect.  (In the past four years, we have built twelve homes.)    As such, it conveys past action that is continuing into the present.  (Or a time period that is not over.) It often comes in sentence opening position, what functional grammar calls MARKED THEME.  (Not the grammatical subject, but a stepping off point for the message structure of the statement.)  I hope that helps.

     Craig Hancock, University at Albany