When I read ''9 to 5'' in this context I take it to represent a culture and mindset of limited engagement and responsibility, not necessarily the literal physical presence for only those hours of the day.
This is the "I got in today at 8:30 and will leave at 5:30 after taking a one hour lunch" mindset or the "Even if I am inspired at 5:20 I'm out of here at 5:30 and if I get into something right before lunch it doesn't matter because I have lunch plans every day" mentality. I don't think people should be overworked, but clock watchers are productivity killers.