There is NO RESTRICTION.........
on how long you need to own a car in order to ship it.............UNLESS, you are looking for some tax credit (ie: Dominican returning home after living in the US for so many years, or a NEW "Resident" bringing belongings over for their "move".........
You can buy a car today and ship it tonight if you want.............
I also believe that the limit was not 5 years but either 7 or 10............and even in that case I have heard of people bringing older cars than that and having to pay a 25% tax fine or something.............I am sure others on DR1 have this info and there is a lot of info here by doing a search of "car shipping".......