How long does it take to hatch an egg?

Hi, my name is Phillip, eggs in Pokemon Mystery Dungeon: Explorers of Sly take from anywhere to 5-8 days to hatch, 7 days average. For example, a Wurmple (a really common Pokemon) will hatch faster compared to a much rarer egg, like a Turtwig, which can learn the amazing egg move, Earth Power. Now you can't always get the move you want. So, in order to ensure it, you reset the game. Save your game by the waterhole and go to Chansey's Daycare. If you don't like the moves, then reset until you do. The gender will always stay the same and you will sometimes find a exclusive three star item. Now, if you REALLY want the eggs to hatch fast, I got a solution. Go to the Marowak Dojo, go inside one of the dungeons, then go to menu, select rest, and give up. This will be treated as a mission complete or one day cleared. Keep doing this at least 7-8 times. Then save at the waterhole and check the Chansey's Daycare. It definitely works!
Sources: My many years of experience.

First, you get the egg on a mission and then keep checking it on and off do a mission and then check again and again.