Ok, I think it would depend on the application form, if it asks the question about disabilites then you would HAVE to declare it at that point (is the question “do you have a disability that requires adjustments to be made” or something?)
If there is no question about disabilities on the form, then I would probably not mention it if it is a hidden one that doesnt effect the work you are applying for. When you get to the interview stage is the point i would bring it up, but state that you are only mentioning it as you feel they should be fully informed, however you can prove it in no way impacts upon your ability to do the job you have applied for