There is no such requirement. They can sell it the next minute after you trade it in if they have a customer.
I would think they are allowed to keep them for as long as they wanted to. Whether they are required to keep them or, not is another issue, that I do not have the answer for.
Infinitely long
I don't know but you might want to check out the following site: http://www.consumeraffairs.com/automotive/dealers_nv.html
How long should a medical record be retained
not reqauired
There is no length of time required before you can trade in a car. Most people wait around one year before trading it in.
A long history of inbreeding and war provocation to keep the empire growing and to keep the opium trade viable.
for 5 years
You might want to ask the dealership that question.
You trade it in for a new one, As long as you have a permit. This only applies if you live in a country where a permit is required.
"http://wiki.answers.com/Q/How_long_it_is_required_for_a_dental_provider_to_keep_past_insurance_explanation_of_benefits"
Owning poultry is an easy task as long as you have everything required to keep them happy and healthy.