Work visa

Hi id like to know if its ok to not yet start for work even if my employer got me a visa already. Theyre waiting for my nhra license before i could start work. And that is taking to long. Im a nurse and will be working in a hospital. I have a working visa and done with lmra and done medical. But they wont let me start work yet. Im locally hired by the hospital. Previously i was holding a visig visa. And converted to working visa after applying to the hospital.