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IV's depend on what route and what time you h/catch it. For example, the third route in the game will nerf your defense depending on which hour it is (so hatching at 11 PM would result in -23 in that stat).
The routes repeat in a pattern, so the 1st route will bork hp, so will the 7th, the 13th, and etc. They go down the list. After one full round, they get lower of the would-be stat in addition to the last one.
1. HP
2. Attack
3. Defense
4. Special Attack
5. Special Defense
6. Speed
7. HP, Speed
8. Attack, HP
9. Attack, Defense
You get the idea
IV's now only go up to 24. The same benefits from max IV's still apply, so 24 is the new 31.
Here's a funny story to go along with it.