I'm trying to get the IV Checker in Ultra Sun, (Still haven't done that yet...) you need to hatch 20 eggs to get it and I want it to take as minimal time as possible. Thanks in advance!
Magikarp and Gyrados, has the least amount of egg cycles at 5. That means it will take around 255*5 steps to hatch the egg. If you breed Pokemon with different IDs they should breed faster too.