"man-hours" is not actually gender specifc. "man" is synonymous to "person", "worker" here.
Think about "mankind". That's everybody.
Imagine a female firefighter saying "I'm not a fireman!" as if it were an insult. Half her colleagues will feel slightly insulted. Fat lot of good that'll do for gender equality.
It's even worse in languages like French or German, where the "feminists" put a female form with gender-specific article next to the old one with a male grammatical gender. Now no macho captain has to suffer that a female can carry the same title, because she's not a "Kapitän", she's a "Kapitänin"!
Congratulations, you've made it easy for people to be sexist.
How can I, as a male, stand up for women's equality, say that it doesn't matter in professional life, when all the time people come up with new vocabulary that cements differences? Honestly, I'm rather fed up with it.