I read that phrase differently again. Yes, there will be things that happen any time in the next 50 years that one might see as a benefit of Brexit. But there is also an emotional/psychological point when people feel better off a result of a change. When will that point be? No one knows. Could be a few months, or a few years, or 50 years or more. None of us know.

But by referring to 50 years I think Jacob was saying if we got to 10 years and that point had not be reached, it is still too early and he cannot yet be blamed: more time is needed. So it is not really about when Brexit benefits can be judged; it is much more about when Jacob can be judged.