Here's another way to see it. Let's get the Unix timestamp for right now:

>>> from datetime import datetime
>>> epoch = datetime(1970, 1, 1)
>>> now = (datetime.now() - epoch).total_seconds()
>>> now
1581261916.910558

Now let's figure out the resolution, by taking the next float up from that value and subtracting.

>>> from math import nextafter, inf
>>> nextafter(now, inf) - now
2.384185791015625e-07

That's 2**-22, or a little bit less than a quarter of a microsecond. We're out from our desired resolution (1ns) by a factor of ~239, so it's going to take another 8 bits (factor of 256) to get us there.