In this manuscript, we explore how tidal properties influence the duration of coastal flooding, and therefore impact. We find analytically that 4 factors impact the duration of the high-water stand: the dominant tide-wave period, the maximum water-level above a datum, the tidal amplitude, and the interaction of diurnal and semidiurnal tidal amplitudes and phases. Some regions—such as the US Gulf Coast—have a combination of tidal properties that leads to long flood durations (>20 hours) for modest inundation depths (e.g., 0.2m). Regions with large semidiurnal tides (such as Gulf of Maine) are inundated for only 1-2 hours, for the same depth of flooding. Within individual estuaries, the potential duration of a 0.2m minor flood event varies by a factor of more than two (e.g., San Francisco Bay, Chesapeake Bay). Combined with relative sea-level rise (RSLR) rates that vary from less than 0 mm/yr to 10 mm/yr around North America, the observed timescale to transition from a zero to two hour flood length varies from 1-87 years. This large spatial variability in tidal inundation properties has implications for hazard planning, ecological adaptation and the future evolution of coastal flood events.