Can i know the validity of the approved visa before getting the hard copy ?

My H1B visa was expired before travelling to US.So I have filed extension and petition has been approved on March10th according to the USCIS website .To get the hard copy of the approved petition , I guess it will take a month from the approved date.So can I know the validity of the visa before getting the hard copy to the employer ?

Only the notice will tell. You will have to wait patiently.