What I have seen in advertising industry, is that people just stay longer. Nothing is ever said, there aren't even any dirty looks if you leave at 5 or 5:30, it is just that you will be first to leave. Then, when someone else does it once, they make an excuse, and you feel like you need to make an excuse.
Fine if you are a contractor, that is the way to work at those places.
I've heard that that is the way the Japanese salarymen put in their long hours. A lot of them end up just sticking around at the end of the day doing nothing. They are just waiting for other people and/or 'the boss' to leave so that it looks like they are being very productive.
Let's hypothetically say we have a young turk in a Japanese engineering department, where the unspoken departmental standard is 6 hours of work in a 16 hour day. If he works 10 hours in a 16 hour day, he is going to quickly draw the ire of his older colleagues, because he is making them look bad. The boss will start cracking the whip and get them to meet or exceed his productivity, and then an arms race ensues. If, on the other hand, he works 10 hours in a 10 hour day, he is going to quickly draw the ire of his boss, because he is leaving six hours before everyone else, despite the project being horrifically behind schedule.
There is an entire genre of aphorisms to tell our young turk. Let's see: the nail that sticks up gets hammered down. The clever hawk hides his claws. etc, etc.
Work diligently, but with sufficient deliberation to achieve the company's exacting quality standards. Document your steps religiously. Hammer out hundreds or thousands of pages of specification documents, since specs always resemble forward progress. Teach your junior employees, who might be ignorant in the way of the world, how things are actually done, and most particularly how they are actually done here. With due deliberation.
Now, of course, my company was totally different, because we would never slack off like that. But, you know, I've heard stories of how things are done at places I don't have near-feudal loyalty towards.
Neal Stephenson nails this game of "Don't go too fast; don't go too slow." perfectly in Snow Crash.
The context there is a US gov employee who has a huge tedious memo in her email. (It's an acceptable use policy on toilet paper use and the prohibited sharing of that precious resource.) We get treated to a long Stephenson treatise on how to properly handle such a memo (skim at a rate that suggests reading rather than skimming, go back occasionally at random intervals - as if rereading details, etc.). It's very well done.
Y.T.'s mom pulls up the new memo, checks the time, and starts reading
it. The estimated reading time is 15.62 minutes. Later, when Marietta does
her end-of-day statistical roundup, sitting in her private office at 9:00
P.M., she will see the name of each employee and next to it, the amount of
time spent reading this memo, and her reaction, based on the time spent,
will go something like this:
Less than 10 min. Time for an employee conference and possible attitude
counseling.
10-14 min. Keep an eye on this employee; may be developing
slipshod attitude.
14-15.61 min. Employee is an efficient worker, may sometimes miss
important details.
Exactly 15.62 min. Smartass. Needs attitude counseling.
15.63-16 min. Asswipe. Not to be trusted.
16-18 min. Employee is a methodical worker, may sometimes get hung
up on minor details.
More than 18 min. Check the security videotape, see just what this
employee was up to (e.g., possible unauthorized restroom break).
Y.T.'s mom decides to spend between fourteen and fifteen minutes
reading the memo. It's better for younger workers to spend too long, to show
that they're careful, not cocky. It's better for older workers to go a
little fast, to show good management potential. She's pushing forty. She
scans through the memo, hitting the Page Down button at reasonably regular
intervals, occasionally paging back up to pretend to reread some earlier
section. The computer is going to notice all this. It approves of rereading.
It's a small thing, but over a decade or so this stuff really shows up on
your work-habits summary.
The sup even times how long it takes each employee to read the email, and makes various character judgements of them based on this time. It was an awesome scene.
Fine if you are a contractor, that is the way to work at those places.