В 80-м выпуске подкаста «Стек-оверфлоу» Джоел и Джефф говорят о том, что нужно считать время, которое реально заняло добавление фичи в продукт. Даже если из четырёх часов собственно кодинг занял 15 минут, а остальное время вы переустанавливали Виндоус, нужно записать 4 часа:

Joel: You’ve got this feature that you do. It took you all morning. It took you from 9 to 1 to do it, because you’ve spent 15 minutes writing the code, and the rest of the 4 hours dealing with idiotic shit that happens all day long because life sucks. It’s the 4 hours that matters, not the 15 minutes [...] The reason everything seems to take forever is that everybody says, well, that seems like a 15-minute feature, and then they put down 15 minutes when they know perfectly well that in real life they would maybe do it in 15 minutes and than they would surf the web for an hour, and then some emergency would happen, and then they’ll have to reinstall their compiler, and then the phone would ring, and then they’ll have an interview [...] and Skype would stop working — all that stuff. And so, what you actually wanna do is measure wall clock time, and that makes it much easier, ’cause you say, fine, 4 hours, ’cause I started at 9 and I finished at 1, and all that other junk can’t be counted agains any other feature, so I’ll count it against this feature, and now you got all these 15-minute features that you estimated at 15 minutes and are really taking 4 hours, and you start to realise that stuff takes 16 times longer than you thought.

Это где-то в районе 45...48 минут.