How much time do i have to return a car if the paper work does not got through?

I live in NJ, and the co signer did not go through and my mom has no proof of address is also not resolved. I'm currently in possetion of the car and have give a 3800 down payment. I'd like to return the car becouse of final numbers i just recently saw. I purchaes on the 27th of august and would like to know how much of a "cool off" period is there to return the car and still get my deposit back.