What's the vibe like in the Engineering dept at Apple? How many hours are you working?

They don't care as much about hours clocked in, as they are about you getting your job done. If you have to come in late because of a dental appointment, or leave early for a child's event, they are really cool about it. The MAIN thing is that you get your work done, and you keep up with your commitments. If you do your work, they are flexible about time. If you don't do your work, it doesn't matter how much time you are in the office. They don't care if you put in 60 hours, if you don't do the work.

Its a lot of fun to work in apple but its a lot of work as well. You are expected to work oncall and after hours / weekends. On the other hand its easy to get time off to do things.

Not very. You are expected to understand the culture. More of a sink or swim situation.