Time between dates
The same span reads very differently by unit. Ten years is 3,653 days, 87,672 hours or 5.26 million minutes. Small units make a span feel large, which is why countdowns to a wedding are quoted in days and prison sentences are not.
How to measure time between dates
The hour and minute figures here assume midnight to midnight, since only dates are entered. That makes them exact multiples of 24 and 1,440 — useful for a rough sense of scale, and not the right tool if you need the gap between two specific moments. Anything crossing a daylight saving boundary also gains or loses an hour in local time, which is precisely why the calculation is done in UTC.
Questions
Days times 24, assuming whole days from midnight to midnight.
No, it works on dates. For exact moments you need a datetime difference.
Not here; everything is calculated in UTC, so a clock change cannot alter the count.
About 525,949 for a common year of 365.2425 days.
Whichever matches how people will act on it. Days for deadlines, years for service, minutes for effect.