July 21 - July 29 is a more important period because we'll know whether SegWit / BIP91 will lock in, and if they do then we'll avoid a split. If it takes longer and protracts into August, there might be panic selling, so I'd say be careful not to buy too early because there might be bad news on the horizon which drive the price down even further. If SegWit2x goes through, the next step is BIP141 and then a hard fork a few months later, IIRC. So wait until July 21, be very cautious until July 25, and if things are looking good, buy.