Ask Pjiang or others about H1b transfer from noncap to cap

I was H1B cap holder and am working at a non profit organization. I understand once I had a cap, I can carry it later no matter I work at non profit or profit organization.

My question is if I transfer from non profit organization to profit company, when I can start working? Can I start working when USCIS receives my application or I need to wait until my application gets approved?

Thanks in advance for your advice.