We now know August 4 is the earliest possible date of a usable hard fork.
The hard fork starts not when the privately mined fork is released, but at the point of its first block. So this means as early as 12 hours an 20 minutes after UASF starts (which is still August 1st).
For those who hold the coins in their own wallet, this may not be as big of a deal. But for those who use an exchange, the recognition of “start time” could introduce unexpected losses.