A System of Logic vs. Mythology: Unlike English, where days are named after Norse and Roman gods (e.g., “Wednesday” comes from “Woden's Day,” for the Norse god Odin), the Chinese system is purely numerical and logical. This reflects a certain pragmatism in the language. Once you learn the pattern (周 + number), you instantly know six days of the week.
When Does the Week Begin? In China, the week officially and culturally begins on Monday (周一, zhōuyī). This is crucial for English speakers, especially Americans, who are often used to calendars that start on Sunday. So, 周三 is unambiguously the third day of the working and school week.
No “Hump Day”: The American concept of “Hump Day”—the idea that Wednesday is the midpoint you have to get over to reach the weekend—doesn't have a direct, widely used equivalent in Chinese culture. While people certainly feel the mid-week drag, there isn't a special cultural term for it tied to 周三.