How long does a doctor have to give me to pay my bill?

I received a bill from them stating that I have ten days to pay. It is the first bill I have received from them. I received it on the 28th, but it was dated 22nd. My health insurance company refused to pay because they want a letter stating that my auto insurance has paid my limit. It will take a few days for my car insurance company to get that to my health insurer and who knows how long for my health insurance company to act on it. The doctor will get paid one way or another, but giving me 4 days, not even really the 10 stated on the letter seems a bit off to me. I thought they had to give you at least 30 days on the first bill before they could charage a late fee or really go after you. Yes, I will make sure they get paid. I did not know my health insurance company would do what they did, I am in the process of clearing the matter up. The letter does not state that they can or will charge me a late fee or go after me if I don't pay by their supposed 10-day deadline. Is this just a scare tatic? What if they don't get paid for 2 or 3 weeks, which is the time it may take to realistically resolve the matter?