Before one can say Jack Robinson

𝗕𝗲𝗳𝗼𝗿𝗲 𝗼𝗻𝗲 𝗰𝗮𝗻 𝘀𝗮𝘆 𝗝𝗮𝗰𝗸 𝗥𝗼𝗯𝗶𝗻𝘀𝗼𝗻 is an 18th century phrase meaning immediately or very quickly, and is said to refer to an erratic gentleman of that name who rushed around to visit his neighbours, rang the front door bell, and then changed his mind and dashed off before the servant had time to announce his name.