I'm at a research centre - not a lab though. It is expected that everyone shows up regularly but there are no fixed times. So some people tend to come early and leave early (9-5), some come late and leave late (11-7 or 8) and some come early and leave late. Some actually only come in the evenings, as they work full jobs "on the side".
Also, some don't come every day, as they have jobs, teach, have a second desk at a different department/university, or have classes. So, really, you never know who's going to be there.
Still, as it is not obvious to have a desk provided to us PhD students at my university, it is frowned upon if you do not show up at all over a stretch of time without giving notice.