I did a deep-dive into how the 1918 Spanish Flu hit San Diego.
Days All Public Places Closed: 37 Days (all places where people congregate: businesses, churches, etc), then they reopened for 12 days which was premature because the flu numbers rose again and they had to close for another 9 days.
Then they quarantined the entire city for 4 days.
Then they backed off and required gauze masks for 14 more days.
But during this entire period, the schools were closed – somewhere around 70-80 days.