How much time to it takes to for amendment process


I have got my H1 stamped 2 months back for NJ location. Now my employer has got some assignment for me in SD. But that position is available only for ~1 month. I have below questions:
  1. How much time it will take to approve the amendment petition?

  2. Should I have to wait till amendment gets approved or I should be able to start working in SD before Amendment gets approved?

I have same question …can anyone reply on this ?