It's been years, but I vaguely remember saving the game at Valley Windworks and then picking it back up months later to find that the Drifloon was there, despite it not being Friday, and it being gone when I reentered the area. Whether or not this is intentional, I'm not sure, but I'd assume it's just an oversight or something with how the game manages saving and time-based events? This is just speculation, but maybe when you save the game and then load it, it loads the same exactly how you left it and doesn't change anything, and when you leave the area it updates the save to how it's supposed to be. I'd bet that if you saved the game at Valley Windworks on any day other than a Friday, and then loaded it back up on a Friday, you'd have to reenter the area before the Drifloon shows up. Kind of like a website or something. If a particular page is changed while you are viewing it, the page won't be updated until you reload it. Maybe the game doesn't treat loading a save the same way a website would treat reloading the page, and instead only reloads it when you leave and reenter the area?
On second thought, this could also be intentional. If the player were to save the game on the tile Drifloon appears on Fridays, and loads the game on a Friday, errors may potentially be caused? Forcing you to leave the area and enter it again before Drifloon shows up would completely prevent that, but it doesn't really explain why Drifloon also stays when you load the game when it was saved on a Friday on a different day.