How soon can I change Employer once a fresh H1B starts?

[[email protected]]

Hello,

I got my H1B approval notice and my visa will start in October. This is the first time H1B after F1 STEM OPT.
How long do I need to wait and work with the current employer before changing to a new one? Do I need to submit salary slips for 3 months "on H1B" from my current employer while transferring?

Thank you.