Ask HN: Do you get more done working longer hours?

I've been wrestling with this idea for a while that pulling long hours at the office doesn't increase the chances of us meeting a deadline. For whatever reason there's rarely more than 4 hours in the day that I write solid working code. The other hours are either meetings or replying to emails. The latter I mostly skip and read HN or Reddit.

What's your experience? Can an engineering team be successful only working 4-5 hour days?