Polynesian
Original Declaration January 7, 2015
First Amendment January 7, 2016
Second Amendment October 21, 2016
Third Amendment March 13, 2017
Fourth Amendment June 2, 2017
Fifth (last) Amendment August 1, 2017
Sold out: ~Feb 2018
Copper Creek
Fully declared: March 13, 2019
From this you'd think that you have at least six months from a DVC resort being fully declared to it being sold out - so at least until September 2019 for Copper Creek. Note that you can still buy a resort after it is sold out, you just don't get any of the bonuses or incentives, and you may have to wait a while before the use year you want is available.
I wanted to answer your question before launching into unsolicited advice like everyone else.
I wouldn't rush into purchasing DVC direct. Ask questions here and on other boards to get insights from current owners, etc. Have you rented points from another owner or a point rental site to try out the resort? That's often a great way of verifying how much you like DVC. Also, it's currently the case that renting points is a better deal than buying DVC direct. There are arguments that this is always the case, but I'll leave it at that.