Office hours are great, right? I try to stick to some sort of routine when it comes to my time in the office, but I also feel the wonderful people who contact me deserve my time and attention in a timely manner. While I'm not going to be answering the phone at 9:00 PM, if I'm awake and an email comes into my inbox I'm going to read it and respond.
If I stuck to a 9-5 email routine, I'd be leaving many emails hanging overnight. I totally understand that not everyone has access to personal email at work; or some may even work second or third shift so contacting me during standard business hours may not be easy. While I do sleep and definitely take some time off to be with my family, I don't see the need to make clients wait just because they didn't email me by a set deadline. They are a huge reason I love my job!