How long would it take to move to "Post Decision"

My H1B has been filed on 23rd May, and currently the status on the USCIS says

"[b]Decision[/b]" with the below content

"[b]On June 7, 2013, this I129 PETITION FOR A NONIMMIGRANT WORKER was approved and we sent you an e-mail notice. Please follow any instructions on the notice. If you move before you receive the notice, call customer service at 1-800-375-5283[/b]."

How long will it take to move to "Post Decision Activity" and is it mandatory for me to wait till its status gets changed else can i go ahead with my VISA stamping request formalities ( like filling in DS160 and getting the appointment".

In the above step it sayd petetion has been approved mine being a PREMIUM processing why would this delay be ?

Didn’t your employer/attorney receive the approval notice in mail? If they have, then you are all set to schedule the interview and appear for the same.