Basically I would love to hear all the details (including minutiae) from when you start the process, to the end.
They take as many days as they need, then come back and conduct a code review of their code with our team. This shows us how they approach coding, how they think through problems, how well they communicate their thinking, how much curiosity they have about the their own solution, how they respond to criticism.
We like this approach because it is much more reflective of how developers actually work than white board or academic type testing. It tells us where their intellectual focus is, their level of humility about learning from others. Surprisingly, what they can teach us. We've had young applicants stump 30-year veterans, which was awesome.
So far, we've had nothing but very strong hires with this approach, and the applicants have all said they very much appreciated how we roll.