before you can say Jack Robinson

Etymology
. There is some speculation that this is a reference to Sir John Robinson, the Lieutenant of the Tower of London from 1660 to 1680 and Lord Mayor of London in 1662, but there is nothing known about him that is associated with speed (Samuel Pepys called him as “a talking bragging bufflehead.”), and the phrase does not appear in print until 1778.

Phrase

 * 1) Very quickly; quicker than one expects.