Months long. But I felt Google was well prepared to help me through every step. I really felt like they cared. I had a phone screen with another designer. Then a week long design exercise. Following that I went onsite for an all day interview with a presentation from my portfolio and 6 separate one on one interviews.

The interview process starts with a initial screen call with recruiter (very nice and professional recruiter introduces what's the next and prep advices. Good time to ask any questions you have), 45 mins long one-to-one design interview with a Staff Interaction Designer to present past case studies and behavior questions(advice: Googlers are trained to help candidates to succeed and they are all really supportive. Be yourself, don't be nervous, and be PREPARED!), Woohoo, panel interview with 4 interviewers from different team, starting with 45 mins long case study presentation in the morning, and comes with a 1:1 design challenge interview, 60 mins long. After that, there will be a 45 mins long collaboration 1:1 interview with designer (normally cross functional), another 45 mins long behavior 1:1 interview with designer( you will be asked questions related to your presentation), lastly, 45 mins long design skill interview (questions still about presentation like how you validate design decision, trade offs, design process etc. ).