I don't know what sort of pattern you're envisioning, but I (and most of the programmers I know) work in bursts. Sure, I can appear to be busy doing the 9-to-5 thing, but a lot of that is being done sort of absently/mechanically. When the light bulb goes on, when the problem that's been running in a background process while I've been absently doing the ritual crap that needs doing is finally solved (or at least a method of solving it emerges), my mode changes. That can happen at any time of the day (or at no time on some days). Just getting that flash into tangible form (let's forget about getting it polished for the moment) takes time and doesn't easily tolerate interruption. And it isn't something that happens at will. It's time to drop this whole mumbo-jumbo "developers are just like factory workers" thing. There may be elements of engineering in what we do, but unless we're working on solved problems, we're creatives with a technical bent.