bajara,
depends on ur lawyer and employer. In my case (Prem. P during transfer), i started after filing it. But then my lawyer had to give the 'green signal' to the employer.
Usually, I have seen people starting with 'receipt Notice'. But then, its always safe to wait until approval.

Ask ur lawyer, ask ur employer, and If they are OK, go for it. Do not wait until approval.

Also, this is the slowest season for H1-B case, so you might get results within a month at the max.