L1B to H1B Visa COS start date as the H1B approved after oct 1st

My H1B petition got approved on 10/9 for the COS from L1B and still waiting to recieve my approval copy. My H1B employeer is different from L1B employeer and looking forward what should be the starting date to start working on H1B.

Can i work on L1B visa for 15 days to serve notice period after recieving the H1B approval notice

Legally, you are required to join H-1 employer from COS effective date. If you work for L-1 for 15 more days, then you run into the gray area. USCIS may question about this period in future and their decision will depend upon your reasonable response. If they don’t question about this in future, then you are all good. Your H-1 attorney can also help w/ this decision.