What factors influence pokemon breeding time?

After some time playing Omega Ruby and attempting to complete my Dex, I've noticed some substantial variability in the time it takes to produce an egg. It got me thinking - what actually determines the breeding time?

I've done some casual looking, but can't find too much on the subject - just some vague notions about compatibility and certain types taking longer. I haven't been able to accurately reproduce a breeding cycle, but I think I've determined a few factors that may influence it:

• Day/night: breeding seems to take a LOT longer after the sun sets. When breeding for a specific nature, during the day I often fill my party with eggs before any of them hatch. When breeding the same pokemon into the night, though, I often hatch 2-3 before gaining another egg.
• Held items: any incense-breeding to produce a baby pokemon seems to reliably take longer than breeding the pokemon itself.
• Marathons: The breeding rate seems to change steadily the longer a certain pokemon is in the daycare. For some, the time seems to increase - for others (mostly starters), the eggs seem to come faster and faster. Not reliable.
• Level: Higher-level pokemon seem to have a slightly higher average breeding time. Not reliable.
• Evolution: Breeding an evolution vs a base (eg Blastoise vs a Squirtle) seems to increase the average breeding time in some cases. Not reliable.
• Type: Type doesn't seem to affect breeding time at all. I've had dragon-types spit out a second egg faster than I could walk away, and I've had a Caterpie take literally 20 minutes to produce.
• Rarity/Power: Very subjective/unreliable. The more powerful/difficult-to-obtain a pokemon is, the longer it seems to take to breed. I tried to benchmark this with a Kangaskhan, Metagross, Gloom, and Wurmple - the first two took considerably longer to produce than the second two. There are definite exceptions (see Caterpie above). This may also just be a function of level/evolution.

This is not a rigorous exploration by any means - I haven't timed cycles or anything. There's also the chance that it's 100% random and I'm basing conjecture on happenstance.

Can anyone tell me what factors actually influence breeding time?

Solution 1:

The chance of an egg being produced is dependent on the Original trainer ID numbers and Species of the pokemon involved.

The day care Man can tell you how likely an egg is going to be generated after each set of 256 steps going on what he says.

Taken from Bulbapedia:

• Same species, Different Original Trainer - "The two seem to get along very well" - 70% (88% with oval charm)
• Same species, Same Original Trainer - "The two seem to get along" - 50% (80% with oval charm)
• Different species, Different Original Trainer - "The two seem to get along" - 50% (80% with oval charm)
• Different species, Same Original Trainer - "The two don't really seem to like each other very much." - 20% (40% with oval charm)
• Different Egg Groups, same gender, or Undiscovered group - The two prefer to play with other Pokémon more than with each other. - 0%

That's all there is to it. It didn't need to change as the generations went on, they've just added more mechanics into it, like IV and nature breeding.