Generally speaking, yes, it does matter. If you are in a car accident and fail to get medical care right away, you may have a harder time recovering fair compensation for your claim. From the insurance company's perspective, you must not have been hurt that bad; otherwise, you would have seen a doctor immediately after the accident. They could use this "delay in medical care" against you. Keep in mind that each case is different, so it would be best to talk with a lawyer about your situation.
It is important to seek medical care after an accident for another reason besides the impact it could have on your case. Failing to see a doctor could put your health in jeopardy! Some injuries don't surface right away and you are much better off getting evaluated by a physician before additional problems arise.
If you were in a car accident recently and you're experiencing medical problems from it, see a doctor as soon as possible. Make sure to tell your doctor about all your symptoms so that he or she makes a record of it.