Precision of time types

Hello,

and yet another clueless newbie question:

The precision of time types is specified as follows in the
documentation:

"For the time types, the allowed range of p is from 0 to 6 when
eight-byte integer storage is used, or from 0 to 10 when floating-point
storage is used."

When/how is the internal storage method determined?

Compile-time option?
Database-initialisation time option?
Other?

Unfortunately, the schema I am trying to implement using PostgreSQL
specifies 9 digits (nanosecond precision) for its custom datetime
column (don't ask me why, I'M just a poor mech eng).

So, do I need to use a numeric type for the seconds and define my own
composite datetime column or can I use a properly parameterized
built-in time type of PostgreSQL?

TIA,

Sincerely,

Wolfgang Keller