Update - Just a few words to explain this news because people keep linking this post. This post was made 12 hours ago, mostly because people kept copying their characters on the old 3.0.8 PTRs servers. 2 hours ago, both EU and US copy page went online at the same time and both had their copy count reset, we can fairly assume that's the 3.1.0 PTR character copy.
However, it doesn't mean that the patch will be released tonight, even if it wouldn't be surprising. (But waiting Monday before testing a huge content patch also sounds like a good idea)
PTR 3.1.0 Character Copy now available
Nothing is official yet, but both european and american PTR Copy pages are now online and the amount of copies available has been reset. Even if it's not officialy 3.1.0 yet. I suggest that you copy your characters while you can because 3.1.0 is coming ... very soon?