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...?
If you are a person who does not take risks then you can choose the date of August 1 as the right time to determine the direction of investment you want. All day is very risky at this time so everything can still happen. Sometimes it is impossible to happen. You have to think carefully in making this decision.