  Social distancing, often in the form of lockdown, has been adopted by many
countries as a way to contrast the spreading of COVID-19. We discuss the
temporal aspects of social distancing in contrasting an epidemic diffusion. We
argue that a strategy based uniquely on social distancing requires to maintain
the relative measures for a very long time, while a more articulate strategy,
which also uses early detection and prompt isolation, can be both more
efficient on reducing the epidemic peak and allow to relax the social
distancing measures after a much shorter time. We consider in more detail the
situation in Italy, simulating the effect of different strategies through a
recently introduced SIR-type epidemiological model. The short answer to the
question in the title is: "it depends on what else you do".
