I would also be interested to know whether this number changes much across different stages of your startup. For example, when you are close to launch, does it get harder to work?
It depends on how much I need to focus on something (and what it is) in order to get it done. Normally: For coding, its probably spans of 75-90 minutes at a time, before a break (20-30 minutes) is needed. After 2-3 periods, food is needed for energy. The cycle can go on for a large majority of the day before sleep is needed. If I'm focusing on design, the spans increase to 1-1.5 hours with the same cycles/time for a break ratio.
I've cut back on my caffeine a lot in the past months, so if I really need a boost, a small amount of coffee/soda/energy drinks will help me out a lot more now then it would have a year or two ago. But once the caffeine wears off, I'm done for the day/night, unless I take more then what I originally took.
Really depends on the day - if I have a lot of interruptions, my "flow" consequently gets shot, and the work I do goes downhill considerably.
However, when I have it going on, I can stay focussed for 2-3 hours at a stretch without needing a break, but generally then my eyes start pointing in different directions. After a short brak / walk outside I can generally pick up where I left off and be good for another couple of hours before I run out of steam...
I _can_ do more than 4 or 5 hours in a day, but not sustainably. I'll occasionally go into "hackertrance" and do a week or mores work in one 15 or 20 hour stint, but I'll usually then need to take a day or two off (or spend a day or two not actually achieving much if I don't). If I push myself to 8 or 10 hours a day of serious thinking work, I'll fade in a few days or so...
It depends on the day. I use multiple timers to track my time, and the correlation goes like this >
The more timers I have correlates to more multi-tasking, and when I multi-task, I usually deflate quicker, so I end up losing steam at around the 6th hour. It takes some coffee to finish up the last two.
On the flip side if I'm working on one or two projects I can go 8hrs with no problems.
I've cut back on my caffeine a lot in the past months, so if I really need a boost, a small amount of coffee/soda/energy drinks will help me out a lot more now then it would have a year or two ago. But once the caffeine wears off, I'm done for the day/night, unless I take more then what I originally took.