If there's a lesson that historical pandemics of influenza provide, it is that earlier (and longer duration) social distancing measures were associated with less mortality and health burden. A review of some evidence:
“The most important conclusion from this work is that the timing of public health interventions had a profound influence on the pattern [of influenza mortality in 1918].” pnas.org/content/104/18… 
"“Those cities acting in a timely and comprehensive manner appear to have benefited most in terms of reductions” in total influenza mortality."
jamanetwork.com/journals/jama/…
jamanetwork.com/journals/jama/…
“Cities in which multiple interventions were implemented at an early phase of the epidemic had peak death rates ≈50% lower than those that did not and had less-steep epidemic curves.”
pnas.org/content/104/18…
pnas.org/content/104/18…
Social distancing and avoiding crowding reduced the “peak incidence of an epidemic and spread it over many, rather than a few, weeks” for the 1957 and 1968 influenza pandemics. ncbi.nlm.nih.gov/pmc/articles/P…
"Mandatory school closures and other social distancing measures implemented in the greater Mexico City area was associated with a 29%–37% reduction in influenza transmission" for H1N1 in 2009. journals.plos.org/plosmedicine/a…
