Here is some information on the creation of Wednesday as 'Hump Day' :
Referring to Wednesday as "hump day” is a fairly modern tradition in American English. The term represents the idea that a week can be visualized as a mound or hill that a person climbs, with Wednesday typically being the middle or peak of the week. There is some disagreement over which day of the week should be the "hump," since it varies depending on when a person works and how a week begins. There are other sources for negative associations with Wednesdays, and few holidays are regularly celebrated on this day.
The Image of a Hump
"Hump day" refers to the idea that a week, especially a work week, is like a hill. Monday and Tuesday are days when a person "climbs" up, since they are the beginning or start of a traditional work week. At the end of Wednesday, the worker has reached the pinnacle of the week, and work on Thursday and Friday represents climbing back down toward the weekend.
This image refers specifically to that middle of the week, where a worker reaches the crest of the uphill journey and begins to pace downward toward the end of the week. Someone with a tedious job or who works especially hard can find it comforting to reach "hump day." At that point, the weekend does not seem so far off as when he or she started work on Monday.
Disagreement Over Wednesday
There is some dispute about whether Wednesday is truly "hump day." When the expression emerged, many people worked a six-day week, and had only Sunday as a day of rest. Some people suggest that in this context, Thursday would have actually been the "hump day."
Looking at the course of a seven-day week that starts on Monday, Thursday is the fourth day of the week and in the direct middle. Yet, many people count the beginning of the week as Sunday, and that makes Wednesday the true middle, regardless of the use of “hump day” in reference to working. For people working a schedule other than Monday through Friday, there may be a different middle day that is appropriate for them.
Negative Associations with Wednesday
Though many may view hump day as a very positive thing, Wednesday has had a bad reputation at times. An old rhyme that describes children born on each day portrays children born on Wednesday as “full of woe.” Wednesday may be thought of as gray days, unhappy days, or unlucky days according to folk literature. Nevertheless, for many working people, the arrival of hump day is cause for cheering, and whether that day is windy or gray, it still means that the weekend is close at hand.