How Charlie and his team convert gold into car in such a short time span in Players?

Of course, the entire car is not made with gold. The only part of the car in gold were the roof, bonnet, doors etc. I.e., the metal parts of car from outside.

The motor car garage owner, Budh Chopra, has manpower and there was pretty much between stealing gold and Russian mafia capturing them. In that duration, making those body parts was not a big deal.

Also, noticed that when Spider catches them, the mini coopers they were riding had no gold. Why? Because Charlie left the cars with gold at Chopra's garage and took replicas.

Here is the transcript:(source)

 So now I understand.
 You left the gold filled cars here.
 And took these empty cars.
 Great, Charlie.

Now, Mr. Chopra only had to make the body parts from gold.