Evidence points to 5 day phase 4, and a 3 day early access. Its not like they need to test anything like some people believe.
What evidence? There is no evidence that supports this, other than one website that said the 17th would reopen beta applications, which was almost immediately removed. If you are really going on this "evidence" assumption, then I'd say the evidence more heavily favors open beta starting much earlier, considering we had the 7 day early access photo, as well as the web page saying that pre-order code registration opens on the 8th.
And actually, they need to test a lot. They have to test the housing system, colliseum pvp, dungeon content post-35, FATE content post-35... well, basically all game content post-35. Obviously it has all been internally tested a lot, but players always find a myriad of stuff that devs don't. It's certainly possible that the open beta doesn't start until the 17th, but stop proclaiming this like you have factual data to back it up. You don't.