[ajnin]

You're assuming a source of monotonic nanotime is easy to get and will always be available. This is not the case. As far as I know you have either "wall time" as usually defined, with all the problems associated with clock drift, NTP syncs, computer going into sleep mode, etc, or "nanotime" which is some time delta from some arbitrary reference and which can only be used to compute time differences and not arbitrary instants in time. One can not be converted into the other easily, or at all.

[Misdicorl]

You use the arbitrary reference and sample the wall clock a couple times to interpolate a best effort offset from utc 0.

If you care more than this, you'll be displeased with off the shelf solutions too