The world isn't quite developed enough to have a high or low tide, but characters could count time between the waves on the beach as one method. Anything that can function as a metronome should work. This change in the setting was spurred by Parsee's efforts to make a water clock, for example.

There is also the withering cycle that happens around Mortis Lake. As this is based on a day/night cycle the two phases should at least be even, so any noticeable discrepancies in that timing will be "corrected" if someone were to point it out. We forgot to update the area's description with that detail, so thank you for the reminder!