L1 to H1 Change of Status and start date

[abhisheksjain]

I am working with Company A on L1 VISA and I have H1B approved with Company B.

Now Company B is filing my COS form L1 to H1 with USCIS.

Can I start working with Company B as soon as I get receipt of filing Change of Status, since I already have H1B approved for company B or do I have to wait for COS to approve with USCIS.

if I have to wait please let me know how much time it take to get L1B to H1B COS to approve when I already have H1B petition approved with company B.

Thanks

Rahul