Background: experienced hire from a boutique strategy firm, targeting an associate role in the Chicago office. Took about 6 weeks start to finish.
Round 1 was two cases, both case partners from the local office. First case was a market entry for a pharma client. Very conversational, they jump in and redirect you a lot. It's not a monologue. Second case was a cost structure one, which I found harder just because the math setup was buried in the prompt. Pay attention to the first 30 seconds.
The PEI question came at the start of each interview, not the end. I got leadership in interview 1, teamwork in interview 2. They really do push on the "what did YOU specifically do" angle. My answer kept drifting to "we" and the interviewer literally stopped me twice to re-anchor to my individual contribution.
Round 2 was with more senior folks. More ambiguous cases, they wanted to see if I could handle incomplete information without spiraling. One case had no numbers until I asked for them, which was clearly a test.
Offer came 10 days after round 2. No exploding deadline but they did note the position had a start window.
If you're prepping: do at least 40-50 cases before your first round. Get a partner who will push back on your structure, not just let you talk. The BCG style rewards intellectual flexibility more than rigid frameworks.