This all depends on who you are addressing in your complaint. If it is an insurance company, you are required to report an accident in a given time frame. This information is not made public and varies for each insurance policy, so it is best to ask your insurance provider about it.
If you plan on filing a lawsuit about an accident, there are different statutes of limitation for each state, ranging from 1 year to 6 years. You can contact Hogan Injury for legal advice about this matter.