AT Kearney: will the offer arrive?

Hi all, I had been invited by AT Kearney to the first round of interviews (2 interviews, both with managers), with the possibility of proceeding to a third round with a partner in case everything was ok.

On the recruiting day, I have done the two interviews, then they have left me waiting some 20 minutes after which they have proposed me to do right away the third interview with the partner (that of course I have accepted to do). I have interpreted it as a good signal, isn't it? What is a realistic timeframe for me to wait and hope for an offer to arrive?

Thanks for your answers.