In 3.10, the expression to convert timespec into inexact seconds appears to
be missing close parentheses for car and cdr.

But I feel that it's better to have timespec as an implementation-dependent
data structure, rather than a pair of integers.  If an implementation want to use a pair, that's ok.
However, an implementation may want to use its own timespec struct to integrate
into the rest of the system (e.g. SRFI-19 time)

We already have timespec-difference and timespec=?, which are technically unnecessary
we do specify timespec is just a pair.   To add (make-timespec seconds nanoseconds),
(timespec? timespec),  (timespec-second timespec) and (timespec-nanosecond timespec),
we can leave the concrete data structure of timespec to implementation's choice.