> How often do you talk about 20 minutes because you can neatly stuff 3 of those time periods in one hour? Dunno. I personally 'visualize' 20 minutes as a thi

> How often do you talk about 20 minutes because you can neatly stuff 3 of those time periods in one hour? Dunno. I personally 'visualize' 20 minutes as a third of an hour. I don't know how common it is to actually stuff an hour full of 20 minute periods, but it happens - you see a schedule with X:00, X:20, X:40. Multiples of 15 or 10 minutes do seem to be more common in that case. But it definitely matters to some extent that it's a divisor. Consider how rare 25 minutes is compared to 20 or 30. If you look at it only as a number of minutes, 25 seems a bit less 'round', but not too much; we often say "25 cents", after all. (And it's 5 squared and a quarter of 100.) But 25 minute periods are less convenient to calculate with, because adding them tends to result in odd/less consistent minute values, because it's not a divisor of 60.