I've had mixed results with more coarsely grained time tracking. On the one hand I'm more likely to actually do so when I don't have to clock in and out all the time. On the other hand, I kept forgetting to clock in or out because it wasn't 'regular' enough to do it automatically.

These days I use Emacs org-mode for todo items and time tracking (+ pretty much everything else), which makes it much easier to be extremely granular in my tracking without having to expend much effort. Since I have my todo list in front of me for any task anyways, starting the clock is just one keystroke away.

That said, I try to keep myself from calculating how much time I 'need' to save to offset the time it took me to get everything set up and to get comfortable with Emacs/Org-Mode ;).