Q: Why can tm_sec in the tm structure range from 0 to 61, suggesting that there
can be 62 seconds in a minute?
A: That's actually a buglet in the Standard. There can be 61 seconds in a minute
during a leap second. It's possible for there to be two leap seconds in a year,
but it turns out that it's guaranteed that they'll never both occur in
the same day (let alone the same minute).