When can we reject employer if 2 cases are approved

I had applied for h1b through 2 employers last year and both were not picked in the lottery.

This year I applied through 2 genuine companies and luckily both got picked in the lottery.

The case status of 1 employer is already approved and the case status of the other employer is not yet updated.

When is the right time to tell the employer not to proceed further with the case? Can I wait for the 2nd employer case status and then decide which employer to proceed with for stamping?

Also, would it be an issue when I go for stamping through employer 1 without rejecting employer 2 ?