I applied in-person. The process took 1 week. I interviewed at Mars (Nashville, TN) in June 2015
Interview
We submitted a project for a consulting program I was a part of to the company and they asked us to continue working for them. They were very eager to hear what else our team had to offer and the interview process was basically just them watching our first presentation knowing what we had to offer.
I applied online. I interviewed at Mars (London, England) in Apr 2019
Interview
Applied Online, had to chase them up for a month before they got back to me. A competency interview with HR and two case studies with consultants, very friendly staff.
I had two interviews on-site in Connecticut, with two different consultants. It took about half a day overall. Everyone was very friendly, and the interviews were very typical consulting interviews -- talking about your background in lots of detail and doing a couple cases. It was a good experience overall.