Because the Earth spins in the same direction as the Moon orbits it, lunar days are 24 hours and 50 minutes long. That means high tides are approximately 12 hours and 25 minutes apart.
Following that logic, we can determine that it takes ≈ 6 hours and 12.5 minutes to go from low tides to high tides, and vice versa.
There are a few ways to go about defining a lunar day. Because the same side of the Moon always faces the Earth, it complicates the definition. We are referring to one full trip around our planet. Nothing more, nothing less. To nail down an impeccably-precise schedule, you’d have to map the coastline, monitor currents, predict the weather and keep an eye out (not literally) for any minor sun movements.