Bipolar counts under ADA rules (US). I wouldn't tell them during the hiring process as you might not be hired. After you are working, you might want to tell Human Resources especially if you need some accommodations.

I had to tell HR when I was a professor at a university and needed a leave of absence. When I returned we made an accommodation plan: no early morning classes, no classes out of town, at least one online class if there were classes I was eligible to teach. When I returned I worked half time and didn't teach... I just had make work. The next semester I was assigned a 9am class, no online class and a class out of town. I lasted about 3 weeks before I had to go on leave again.

When I returned from the first leave, they required me to sign an agreement that I would not disclose my diagnosis or symptoms to any faculty, staff, or students. They said I couldn't come back if I didn't sign it. I talked to someone in ADA and they said although it was wrong, they don't get involved unless the action causes a loss of income. So if I hadn't signed it and hadn't been allowed to return to work then I would have had a case. Also you only have 9 months to put in a claim, I think.