What is best time to apply for h1 b transfer when my F1 is going to expire


I have a question regarding h1b transfer and hope to get an answer here.

I have applied for h1 through my current employer and I even expediated the process by premium processing, but i dont know the status yet. I want to apply for h1 transfer through another employer once i hear the status of my present h1 processing. My question is that my F1 visa stamp is going to expire in december 2012, in order for me to apply for h1 transfer through the new employer do I need to have the F1 valid stamp? what will be the best time for me to apply for h1b transfer with the new employer?

Any help highly appreciated.

Thank you.

You may transfer your H1B to another employer as soon as the petition is approved. You may expedite that process to PP and start working on 1st October.