If launch is around August 27th then we can guess as to when phase 4 will end. Yoshi has stated that the early access will lead directly into the release so that bumps us a week back to the 20th. He also mentioned that there was only going to be two to three days between early access and phase 4 so that bumps us back to August 17th. If the open beta is two weeks long (it may be shorter), we can assume that it will start around August 3rd. This could mean that if next weekend is the last test of Phase 3 and it lasts a full week, we will have about three weeks between Phase 3 and 4.
This is of course all speculation, even though it is based on comments made by Yoshi and official posts regarding scheduling for phase 3. They could very well push the launch date back, but I doubt it. Thank god they don't listen to people on beta forums that write a book of text stating that they should postpone the release simply because the Limit Break system is not to their liking and therefore gamebreaking.
FFXI: DamienSlvrblade Race: Elvaan Nation: San d'Oria Server: Sylph 2002-2007, Phoenix 2012
PUP WHM PLD MNK BLU BST SAM WAR BLM 99 BRD THF NIN DNC SMN RDM 50+
FFXIV: Damien Scott Race: Duskwight Elezen GC: Limsa Lominsa Server: Ultros
DoW GLA50 ACN50 PUG50 MAR 50 Rest30+
DoH/DoL All 40+