If it simply says they don’t like each other much they’ll still breed. You can’t change their compatibility as far as I’m aware of, but it shouldn’t prevent them from breeding. The only Pokemon who won’t breed are Pokemon of different egg groups and from the Undiscovered egg group, but since you’re using Ditto and Golett, it should be able to work.
Oh, and for how long it will take, I found another db answer for that.
If they are from the same original trainer, the day care man will say, "The two don't seem to like each other that much." (or something similar)
This means that every 256 steps you take, theres a 20% chance of getting an egg
This also states a piece of information I forgot to add about why you can’t change the compatibility of the Pokemon: it’s judged by both Pokemon being from the same original trainer or not.
Oh and another little detail: in BW2 they introduced the Oval Charm to increase the chance of getting an egg, but since the question is tagged “black” I’m guessing you don’t have access to it.
Hope this helps and good luck <3