First make sure every Hidden Grotto is filled with something. If you haven't touched them yet, the only one you need to worry about is the one with the Minccino.
Go into your Grotto-of-Choice, empty it, and save in it.
Use the Hidden Grotto Timer Finder in your RNG Reporter (or PPRNG, but we aren't really familiar with it) to find a good seed. Let the
Hidden Grotto Encounter Tables help you.
As you can see, Ditto is in the 0th Slot and in all four SubSlots of the 0th slot. Search!
You will find lots of choices, so pick one you are comfortable with. Dittos are genderless, ignore the gender ratio. For future reference: That's where the gender is determined.
Turn on your game at the date of choice. Once you are in, walk 256 steps to generate a new Grotto content. A Max Repel may help you count for 250 steps.
Leave the Grotto and re-enter it; there should be a Ditto, otherwise it means you have got the wrong Timer0. Repeat the process until you have successfully generated a Ditto.
For the IVs, do the usual stuff: Go back to the Capture tab of the Time Finder, select the Hidden Grotto Encounter Type and your preferred IV spread (and Hidden Power! and 31 HP). Take the seed, back to the main screen, select Nature an so on. You should be familiar with it.