The bad roundings that appear in #7138 (loss of microsecond precision for dates around today) make me wonder whether we should just switch to using float128s everywhere for date-related data.

Time is encoded as seconds since 0001-01-01 UTC, so float64s (53 bits) can keep microsecond precision for a timedelta up to 2**53 / 1e6 / 3.154e7 ~ 285 years (3.154e7s/y), which does not go up to today. On the other hand float128s offer 113 bits of precision, i.e. ~3e20 years -- that should be safe, even if we switch to nanosecond precision :-)

On the other hand I don't actually ever use dates in plots so I don't know if it's really worth it.