All day. Groups of 2 or 3 engineers at a time came into a windowless conference room and asked questions. Some of them involved solving logic problems, either with writing code on a white board or a flow chart showing how you'd solve the problem. It's pretty grueling. I was asked about projects I've worked on, and apps I've made. In hindsight, I would have had my Xcode environment ready on my laptop (I was not developing on my laptop at the time, so it had an older version of Xcode without code completion, which I use a lot now). They sometimes said I could use my laptop rather than the white board if I was more comfortable with that, and I am.