H1B Petition 2015 Approved,Not Stamped Yet- Can i have other employer get me stamped?

USA H1B Visa
1

I have a H1b approved Petition from my current employer, not stamped yet… Is it possible for me to switch and get stamped from another employer without waiting for lottery again ?

2

It have to be stamped from your current employer then go through H1B transfer later if you want to change employer

3

Thanks ! This helps

Other Query that i have is:

My H1b Petition is approved with expiry date as 30Sept2015. Few Questions i have:

  1. Will my visa be valid for a date not more then Petition Date?

  2. Once i am in US, and my Petition Expiry date is approaching, do i have to come back to India for Visa and Extension or the same can be done from USA only?

  3. Is there a time limit till when i should get my stamping done before petition expires?

Please help me with this.; Really tensed.