noon, midday, moment, land measure
晌 centers on the middle of the day: noon or midday. The meanings 'moment' and 'land measure' are less common and may be separate, unrelated senses.
晌 combines 日 (sun) with 向, which likely contributes the sound and the idea of direction or facing. The character originally referred to the time when the sun is directly overhead, i.e., noon.
The sun 日 faces 向 directly overhead at noon. Picture the sun at its highest point, casting no shadow—that is midday.
For ショウ, imagine the sun showing its full strength at noon: show -> ショウ, and the sun is directly overhead.