My view - as a geek and a manager, is that unless you are one of the rare people whose job does not involve interaction with others, then there should be a standard set of core hours that a person is available in the office. My personal view is that it is reasonable to expect people to be available between 9 am and 4:30 pm, with some time off for lunch.

I have for a long time (all of my 20+ years of working) been in places where there was flexible working hours. Any place that does not have some degree of flexibility is way behind the times. I start at 7:30 each morning - I get about 1 hour or more of relatively undisturbed work, and if I decide to leave early (say 4:30), I have still put in a good day.

The bottom line is, you have to be seen to be dedicated, and not just doing your own stuff, but working ith others in your team, users, and the rest of the people you should be interacting with.