The bolded phrase can't be measured. With block chains we don't know when is when. All we know is the longest chain and what was confirmed in each block. As you know, there is no global clock to compare chains. This insight is fundamental to understanding block chains at the research level.
As I explained in the post of mine you quoted from, the only way to measure relative time between two block chains is during propagation, but you and I already documented in my vaporcoin's thread that propagation doesn't prove anything (can be inconsistent among peer nodes and offline nodes can be lied to).
I'm not entirely sure you need time at all for this. For the sake of argument, imagine we have our awesome new chain selection rule in place already, which selects the chain with the largest set of transactions. If the majority POW starts censoring transactions and produces a block with a subset of all transactions, the minority can produce a competing block at the same height which contains the attackers transactions and the censored transactions.
Now, logically at this point, the attacker would simply use his superior POW to generate a bunch more transactions to fool the chain selection rule, however, again, the minority can simply include these new transactions and the original censored ones thereby producing the largest set again.
This might end up in a stalemate of infinite forking, of course as attacker and minority battle it out forever, but there we are.
Yes of course was one of my ideas long ago, but as you have identified there is still an ambiguity because as soon as we accept the minority chain, then the longest chain announces a new block with more transactions. There is never a point in time where we know definitively which chain is longer in number of transactions.
So let's say the union of both chains is the rule. The problem becomes how many chains do we allow in the union because it is unbounded. If we place a bound on it, the adversary can Sybil attack the bound.