Datetime is represented in, so called, external TAI64 format.
TAI stands for Temps Atomique International, the current international
real time standard. Unlike UTC, it takes leap seconds into account,
making it monotonous.

=> TAI64
=> TAI

You can convert TAI to UTC by subtracting number of leap seconds.

TAI64N format adds 32-bit big-endian number of nanoseconds
(up to 999999999) count.
TAI64NA adds another 32-big big-endian part of attoseconds count.

Shortest form *must* be used: if number of nanoseconds equals to zero,
then use TAI64 format.

Example representations:

1970-01-01 00:00:00 TAI             | 18 4000000000000000
1970-01-01 00:00:00 UTC             | 18 400000000000000A
1969-12-31 23:59:59 TAI             | 18 3FFFFFFFFFFFFFFF
1992-06-02 08:07:09 TAI             | 18 400000002A2B2C2D
1992-06-02 08:06:43 UTC             | 18 400000002A2B2C2D
1997-10-03 18:15:19 TAI             | 18 4000000034353637
1997-10-03 18:14:48 UTC             | 18 4000000034353637
2016-12-31 23:59:59 UTC             | 18 40000000586846A3
2017-01-01 00:00:00 UTC             | 18 40000000586846A5
2024-11-20 12:19:08 921772500ns UTC | 19 40000000673DD3E136F121D4