[ORAS] Eggs hatch faster when their parents are in the team

[Puzzlemint]

This might already be common knowledge, but I stumbled across it just this morning, and can't find any mention of it anywhere.

I haven't tested this thoroughly or in detail, or in any game other than Alpha Sapphire, but so far the results are consistent.

With both Natu eggs (bred from Xatu x Zubat) and Budew eggs (bred from Roserade x Pikachu), having both parents in the party, as well as a Slugma with Flame Body, seems to cut hatching times by about 75%, compared to having just the Slugma and neither parent.

Other thoughts:
Does it require both parents?
Can it be either? Does it have to be a specific parent?
Is having both parents more efficient than just having one?
Does this work in older games? And newer games?
Am I just losing track of time and completely imagining this?
Does everyone already know this and I just completely missed out somehow?

 

[Stratelier]

The only way this would make sense is if the offspring Pokemon's data has some internal record of its parents (compare and contrast: it does record the Pokemon's birth moveset, enabling you to reteach them at a Move Reminder).

Have you already checked for other potential factors (like O-Powers)? Max Level Hatching power doubles hatching speed and stacks with Flame Body, which would also reduce overall time by 75%.