In 5 years, I worked at 3 different agencies plus an internship makes 4. In my experience, every agency is different and every small office within the agency is different.
I've worked in offices where:
-You wrote in the exact time you came in and left down to the minute. 8:28 to 4:58 if metro was early that day.
-I've worked in agencies where you worked your 8 or 9 hours and went home. No clock-watching but it also was expected if you stayed an hour late that you would get credit hours.
-And I've worked in offices that are whatever it takes to get the job done with smart phones making it a 24/7 style gig.
My sense is we are moving more towards the later in government and the rise of blackberries contributes to that. At the beginnning I saw blackberries being distributed only at the high levels - GS-15/SES but I've seen it trickle down so it seems like almost every employee has one.