Is it me or did Gavin ignore Yifu's direct questions? In case you missed it Gavin --
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"We can look at the adoption of the last major Bitcoin core release to guess how long it might take people to upgrade. 0.11.0 was released on 12 July, 2015. Twenty eight days later, about 38% of full nodes were running that release. Three months later, about 50% of the network was running that release, and six months later about 66% of the network was running some flavor of 0.11."
On what grounds do you think it is reasonable to assume that this update will roll out 6x faster than previous data suggested, as oppose to your own observation of 66% adoption in 6 month. or do you believe 38% node upgrade-coverage (in 28 days ) on the network for a hard fork is good enough?
There are no harm in choosing a longer grace period but picking one short as 28 days you risk on alienating the nodes who do not upgrade with the aggressive upgrade timeline you proposed.
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When Gavin writes "Responding to "28 days is not long enough" :
I keep seeing this claim made with no evidence to back it up. As I said, I surveyed several of the biggest infrastructure providers and the btcd lead developer and they all agree "28 days is plenty of time."
For individuals... why would it take somebody longer than 28 days to either download and restart their bitcoind, or to patch and then re-run (the patch can be a one-line change MAX_BLOCK_SIZE from 1000000 to 2000000)?"
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Isn't Yifu's comment, evidence, the very best sort of evidence, it isn't propositional a priori logic, but empirical evidence that. As for why people take longer, who knows, we simply know from passed experience that it in fact does take longer.
It's extremely frustrating to read Gavin's comments, it's hard to believe he is engaging in earnest discussion.