Laid off and currently under 60 day H1-B grace period. A receipt generated suffice to be in status or need to start working?

I am currently under 60 days grace period after lay off starting January 1, 2021. An employer is currently transferring my H1-B visa in premium processing.
Employer is willing to give a start date only after the petition was approved by USCIS as per their policy.
To be considered in status after the 60 day grace period on H1-B, should a receipt number generated within the grace period be enough (or) should one start working for the employer on the receipt before end of the grace period?