all the announcement had to say was: June 30th to 10 am July 14th.

----|
or July 14th 10 AM CST.

simple
why had stuff?

10 am central standard time is 8 am for folks on the West Coast, so for all practical purposes the entry period ended on the 17th. 
As I recall I  made a quick visit to the contest page when I first saw it to see if it required any special items to be used. But obviously I wasn't looking for info about when the entry period ended. 

I've gotten worked over by companies whose "the contest ends the 21st" meaning 12:01 am (which by the way is how your car insurance usually works). 

But since I was accustomed to being able to get the days specials up through midnite CST -- I admit I assumed July 18th was July 18....
 

apparently July 18 end of contest unlike July 18 end of sale means closing earlier in the day.
Having corralled some time to work on an entry,
not pleased to be told on July 18 --- you don't have permission to access the entry page... 

Round 1 :: Swimsuit Competition

Entry Period: June 30th - July 18th.
Community Voting: July 19th - July 28th.
Submissions can include 2D or 3D.
Winners from Round 1 will be announced on July 29th and will advance to Round 2.

Things may be different back East, but in Oregon it's still July 18th 

also on the first page of checking out with the display on stuff added to prime across the top... right clicking on an item and saying open in new tab... opens a duplicate of the page.

while checking the stuff on the first page of checkout, I went back to the plain shopping cart page where it now has a message across the top that says:
Caught exception: It appears this item is already in your cart. 
doesn't say which item and if I reload the cart from drop down menu it shows all the items with no message. 

top is cart after going back from page one of checkout
middle is a fresh cart
bottom shows item already purchased