Been discussing this on BG.
IF it starts on August 17th, then unless Yoshi-P shortens the length of OB, then Early Access has, at maximum, a length of three days.
August 17th - August 23rd
August 24th - August 27th
Something doesn't add up there. There is literally no time between OB and Early Access to fix any issues. I'd estimate Phase 4 would start on the 14th at the latest, just so the Dev Team would have at least 3 days to fix anything, then use the weekend as Early Access.