It's usually a very individual decision. It also depends on where you work and the age of your co-workers. My younger co-workers would arrive like 9:30 for breakfast, and leave at like 7-7:30 after dinner. I've also worked with people who would get in at 11 and leave at 8 or 9. Older co-workers with families will generally work a 9-6 or something, and often won't stay for dinner (but may occasionally bring their families for dinner :p)