Over the past two months, I've had the opportunity to work from home. I've spent the last six years working in an office environment, with the standard "open" workspace.
Within the few months of working from home, I've noticed a radical change in my day. No longer am I interrupted randomly, while in deep thought. I don't veer off to the break room for coffee, and get caught up in conversations. I don't take excessive lunch breaks to stand in lines at a restaurant. Speaking of, it helps the waistline! I have easy access to my full kitchen at home. I digress.....
Anyway, my team is located in central time, so I reap the benefit of distraction free coding between 2PM and 7PM pacific time.
I typically wake up, sit down at my desk at 9AM, and begin my daily routine of checking email, checking out what's new via HN, catching any meetings with folks in the central timezone, etc. Once lunch comes, I take a break, and begin planning what I want to accomplish in my 2-7 distraction free time block.
So, while I do work a full 8 hours, only about 4-5 hours of that time is spent head down in code.
Point is, I certainly agree working 4:30 is probably sufficient, however, for me, I do utilize the other hours of the day to "socialize" and plan "big picture" with my colleagues via video conference. I feel that if I lost the extra time in the mornings, these meetings would overflow in to my distraction free time.