It depends. If the Pokemon are from the same game, for every 256 steps you take, there is a 19.8% chance that there will be an egg at the DayCare. If they are from different games, then it is a 49.5% chance for every 256 steps.
Source
Depends on the genderless Pokemon, here's a guide for each one: http://bulbapedia.bulbagarden.net/wiki/Egg_cycles I believe you are looking for egg cycles, then steps are the number of steps needed to hatch the egg. If you breed with ditto and another Pokemon, what will hatch out of the egg is the Pokemon that is not ditto, so look for the genderless Pokémon's info on the guide. Hoped I helped!:)
It matters what the day- care man says if he says they dont like them much or something they have a low chance of a egg if it says they dont play with them then they wont have a egg. If your talking about a mew and ditto or something it cant work Why? Because it is a lengedary Pokemon and they cant have eggs if your talking about manamphy it can it has a low chance
I hope I helped you
