As an experienced engineering manager this is what I've come across - Some of the engineers who put a 9 to 5 clause, are usually the obstinate engineers, who are not very productive during the hours of 9 to 5, but won't make up by working extra hours. The motto is 'This is all I'll deliver, live with it'. Perhaps, this bias factors in and a generalization emerges 'All 9 to 5 engineers are stubborn, non-creative, non-committed'. This is a huge fallacy because, again based on my limited experience, I have worked with some of the most productive, creative and committed engineers who mostly worked 9-5, but sprang to action in the middle of the night when a high priority production bug had to be looked into.