the period from 1 to 3 am, 2nd character of the "branches"
丒 is a rare character used in the traditional Chinese timekeeping system to denote the second of the twelve Earthly Branches, corresponding to the double-hour from 1 to 3 am. Its meaning is entirely tied to this calendrical role.
丒 is a variant form of 丑, the second Earthly Branch. The exact historical development of this particular shape is uncertain, but it likely arose as a graphical simplification or alternative writing of 丑.
Think of 丒 as a stylized ox horn (丑 is associated with the ox in the Chinese zodiac) with an extra line marking the late-night hour. The shape suggests a horn pointing upward into the dark sky between 1 and 3 am.
For チュウ, imagine the sound of a clock chiming twice in the deep night: 'chu-chu' — the second chime marks the 丑 hour, cueing チュウ.