This thread hits close to home. My girl and I (both daily pg players) have this inside joke that began a month or so ago after notice the same thing.
While I cannot backup the "2 day" theory, I can say that our joke is based around the theory that:
"I betcha that after walking this "Larvitar" 89km and finally get my first Tyranitar, I'll hatch one from my next 10km egg with like, 32 candies"
"Lmao. OMG! How mad would you be?"
Next 10km hatch...Larvitar...with better IV's!!! Lol. It's probably just a strange human brain event. However, just like this thread implies, it sure feels like there's something too it!