Wiktionary
before you can say jack robinson
adv. (context idiomatic English) Very quickly. Quicker than one expects.
Usage examples of "before you can say jack robinson".
You are bowling along on a wind that's as steady as a sermon, and just as likely to last, and before you can say Jack Robinson the wind whips around from weather to lee, and if you don't jump for it, you'll have your canvas blown out of the catheads and sailing for heaven in rags and tatters.
I'll clap the darbies on that gentleman before you can say Jack Robinson!
And they'll be after it in one of their big flashy cars before you can say Jack Robinson.
Our two romantic leads are wolf meat before you can say Jack Robinson.