Capt. Scumbalino wrote:

It's based on the pretty-much universal fact that the time for the tide to
change from high to low water, and vice-versa, is pretty close to six hours.

Universal, if your universe consists of only places with semi-diurnal
tides. That's the majority, granted, but not everywhere has
semi-diurnal tides.

You might want to get out more.

//Walt