L1B to Cap Exempt H1.Work using Receipt notice(or)Should it be approved?

Hi Saurabh and Experts,

I had an approved H1 WITHOUT COS.

I’m currently working on L1B.

Now trying to convert L1B to Cap Exempt H1 using Premium processing for L1 employer.

I-94 of L1 will expire by Mar 15th.

Once H1 is filed and if not approved by Mar 15th; Can I work using Receipt notice of H1 (or) should I only work after H1 is approved?

Any response would be highly appreciated.