I disagree with the importance of this concern and old soft/hardforks will
replace this activation mechanism with height, so that's an argument in
favor of using the height from the start. This is "being discussed" in a
thread branched from bip99's discussion.
Anyway, is this proposing to use the block time or the median block time?
For some hardforks/softforks the block time complicates the implementation
(ie in acceptToMemoryPool) as discussed in the mentioned thread.
On Sep 19, 2015 1:24 AM, "Rusty Russell" <rusty@rustcorp.com.au> wrote:

> Jorge Timón via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
> writes:
> > I agree on using height vs time. Rusty, what do you mean by being easier
> > for bip writers? How is writing "block x" any harder than writing "date
> y".
>
> Three years from drafting is reasonable.  How many blocks is that?  Hmm,
> better make it 6 years of blocks just in case we have a hash race.
>
> Deployment speed is measured in months, not blocks.  It's hard enough to
> guess without adding another variable.
>
> Cheers,
> Rusty.
>