What is a tide clock and how does it work? Fun facts: The lunar day is 24 hours and 50 minutes long & the moon is the biggest influence of the tides! Since there are two high tides each lunar day our tide clocks rotate every 12 hours and 25 minutes. Quartz tide clocks are perfect for the more predictable tides of the Eastern United States. You can always set your tide clock by either a quick internet search for high tide in your area for the next high tide, or set it monthly at the full or new moon.