Half day cycle?

Hurst’s nominal model allows for a daily cycle and then a roughly 5 hour (320 minute) child cycle to the daily. Is this meant to be a tripartite cycle like the 18 year and 18 month child cycles are to the 54 year and 54 month parents or is there another cycle to make up the gap?

Even if we look to fit three 5 hour cycles in a day there would need to be considerable variety in the cycle lengths to fill roughly 27 hour daily cycles.

Did Hurst mention a roughly 11 hour cycle that would approximately bisect a day?