I have edited my response (2-up), effectively saying I was wrong with hard fork date for segwit2x (I had assumed the hard fork was simultaneous put live with segwit activation). Instead, segwit will be activated when/if sufficient miner votes made. However, the hardfolk will be activated either September 21st or 3 months after this. As explained by "jgarzik":
The prediction is that miners activate rapidly, therefore, block 485218 (BIP102_FORK_MIN_HEIGHT) becomes the hard fork point. "+3 months" is the fallback safety measure, in case activation is slower than predicted.
See this thread for further details:
https://www.reddit.com/r/btc/comments/6i16gl/psa_how_segwit2x_actually_works/(definitely worth a read if any of you are concerned by this!)