Match Day, as its name states, is the day that a competition is played. In other words, is the day that an athlete gets ready to compete.
The schedule of a Match Day depends on the sport and time of competition. However, it is true that for a competition, you get ready throughout the whole day.
If you compete in the morning, you will have to wake up early, take care of your body, get some rest the previous night and food before the competition. If the game is in the evening, you will have to get mentally and physically ready throughout the whole day to be ready when the time comes.