It looks like the biggest uncertainties will be resolved this Friday, July 21st. With far above 80% support for SegWit2x, August 1st should not matter anymore (as BIP 148 will not trigger).
That would mean between now and Thursday should be the best time to buy.
On the other hand, August 1st is passed around everywhere as the "day of doom." Many uninformed people out there. So maybe wait till July 31st to buy? And will there be any risks left after Segwit is activated later this week?
The key question is: How much FUD will be left in the market after Friday...?
It has already begun. It was earlier than expected:
The Bitcoin Scaling Countdown: Miners Begin Running Segwit2x Software
It seems July 17 has initiated the beginning steps towards Segwit2x activation as the code has been released and miners who supported the New York Agreement (NYA) have started running the new BTC1 software.
source:
https://news.bitcoin.com/bitcoin-scaling-countdown-miners-segwit2x-software/Wohoo. I' excited for this. Let's hope that it will all the uncertainty now.