This start time seems reasonable to me. It is mostly in line with BIP 9's
proposed defaults, which seems like an appropriate choice.
On October 16, 2016 10:31:55 AM EDT, Pieter Wuille via bitcoin-dev
>We're getting ready for Bitcoin Core's 0.13.1 release - the first one
>to include segregated witness (BIP 141, 143, 144, 145) for Bitcoin
>mainnet, after being extensively tested on testnet and in other
>software. Following the BIP9 recommendation  to set the versionbits
>start time a month in the future and discussion in the last IRC
>meeting , I propose we set BIP 141's start time to November 15,
>2016, 0:00 UTC (unix time 1479168000).
>Note that this is just a lower bound on the time when the versionbits
>signalling can begin. Activation on the network requires:
>(1) This date to pass
>(2) A full retarget window of 2016 blocks with 95% signalling the
>version bit (bit 1 for BIP141)
>(3) A fallow period consisting of another 2016 blocks.
>  https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki
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