Usually Blizzard is pretty definitive when they take something down. However today they've decided to take down the PTR (Public Test Realm) in the morning, and then put it back up early tonight. I'm reminded of a recent Simpsons episode I watched where Homer is sitting in his hospital bed awaiting a heart bypass surgery and goes "Bed goes up, bed goes down. Bed goes up, bed goes down." PTR goes down, PTR goes up.
All of these announcements come from the same person, Hortus, so it's not an issue of him being confused or anything (unless the whirly jig in his head has gotten to him). Hortus does tell us that they've put it up for "some additional testing," which really isn't a surprise given it's a test realm.
This probably means that patch 2.4.2 won't go live tomorrow if there is maintenance. Once we know more we'll post and keep you updated.