Per my fading memories irt hurricanes:

For a moderate event: A week for the undamaged stores to open. That accounts for the return of employees and restocking of shelves, plus the restoration of electrical, water, sewage, & communications.

1) Strictly depends on the severity of the disaster vs. gov't response in restoring basic services + law enforcement.

2) Poor response means people are slower to return, cleanup is delayed. Some businesses may never reopen.

3) No American city has more than 3 days supplies in it. Supplies are usually bought up within 3 hours of the public realizing that a forecastable event is approaching. A forecastable event may be a hurricane, ice storm, blizzard, flooding, etc. An unannounced event may be a HazMat incident (rail, waterborne, highway), tornadoes, earthquake, terrorist attack, etc.

4) Beware the Stobor!