Most of the United States coast is semidiurnal: two high waters and two low waters in each lunar day, which runs about 24 hours 50 minutes rather than 24. Because that is longer than a solar day, every tide falls roughly 50 minutes later than its equivalent yesterday, and the whole pattern walks forward through the clock. That is why a calendar day sometimes holds only three of the four events, and why no fixed time of day is ever the answer.
Two of each, on most of the coast
The tide is a very long wave, and on most of the US coast the basin responds to the moon twice a day. That gives two high waters and two low waters, spaced about 12 hours 25 minutes apart, which is half the lunar day. The pair of highs are usually not the same height and neither are the pair of lows: that inequality is why US charts are measured from MLLW, the mean of the LOWER low waters, rather than from the average of all of them. On any given day the difference between the two lows can be a foot or more, and on a big-range coast a good deal more than that, which is what decides whether a flat uncovers in the morning or the afternoon.
Some coasts get one, and some get one and a half
Parts of the Gulf of Mexico are diurnal: one high water and one low water a day, because the basin's own resonance responds to the daily rather than the twice-daily part of the tidal forcing. Other stretches, including parts of the Gulf coast and the Caribbean side of the country, are mixed, where two events a day happen but one pair is so unequal that in practice the day reads as one useful rise and one useful fall. The type is a property of the place and does not change, so once you know which one your beach is, it stays true.
How often the pattern itself changes
Two cycles sit on top of the daily one. The first is the spring and neap cycle: around new and full moon the sun and moon pull in line and the range is at its largest, and at the quarters they pull across each other and it shrinks. That repeats about every 14 days. The second is the moon's distance, which brings its closest approach round about every 27 days and pushes the biggest spring ranges higher still. Neither changes how MANY tides there are in a day; both change how big they are, which is usually the number that actually matters for a plan.
Questions people ask about how many tides are there in a day
How many high tides are there in a day?
Two on most of the US coast, about 12 hours 25 minutes apart, though a calendar day occasionally holds only one because the lunar day is 50 minutes longer than the solar one. Parts of the Gulf of Mexico are diurnal and get one high water a day.
How often do tides change?
The water turns roughly every six hours and twelve minutes, so a full cycle of high to low to high takes about 12 hours 25 minutes. The times shift about 50 minutes later each day, and the SIZE of the range cycles over about 14 days between spring and neap tides.
Why are the two low tides different depths?
The moon is rarely directly over the equator, so the two bulges the earth turns through in a day are not symmetrical about your latitude. That produces the diurnal inequality: one low is lower than the other, and US tidal datums are measured from the mean of the lower ones for exactly that reason.