What does “Brexit times five” mean? Is “X times five” a popular idiom to mean a big number / impact / difference?

Solution 1:

Yes, it is common to say " something times something else" to express the idea of an amplified effect:

times

• used as a multiplicative word in phrasal combinations expressing how many instances of a quantity or factor are taken together: Two goes into six three times; five times faster.

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Brexit was an unanticipated and very surprising result to many Europeans, Trumps victory will be five times as much for many Americans and possibly for many foreigners.

From Vox.com:

• Trump told rallygoers that the results on Election Day will “be like Brexit times five.” Newt Gingrich says Trump’s odds of winning remain “very, very good” because “just as with the Brexit vote in Britain,” there are secret Trump supporters out there who don’t want to tell pollsters they are voting for him. Matthew Goodwin at Politico exhorted liberals on October 16 to “learn the lesson of Brexit” and not underestimate Trump’s chances of winning.