H1B 問題

I currently hold F2 status and before this I had H1B visa. After I quit my job, I successfully transfered my status from H1B to F2. Now I got a job offer from a company which will sponsor my new H1B application. I am not sure when I can work. May I begin to work for the company after my H1B case is filed or I need to wait for the approval of my H1b application?

Thanks for any help!